Attachment 361522 Details for Bug 193919 – Patch

[patch] Patch

bug-193919-20190209011653.patch (text/plain), 208.36 KB, created by Alice Mikhaylenko on 2019-02-08 12:16:56 PST

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Creator: Alice Mikhaylenko

Created: 2019-02-08 12:16:56 PST

Size: 208.36 KB

patch

obsolete

>Subversion Revision: 241197
>diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
>index d5a70a10ed716cc9d8dab348da821defc446ee9e..b2db167bcd95b7f6e09caa97ebf19bed8ae45373 100644
>--- a/Source/WebKit/ChangeLog
>+++ b/Source/WebKit/ChangeLog
>@@ -1,3 +1,276 @@
>+2019-02-08  Alexander Mikhaylenko  <exalm7659@gmail.com>
>+
>+        [GTK] Implement back/forward touchpad gesture
>+        https://bugs.webkit.org/show_bug.cgi?id=193919
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        Move ViewSnapshotStore and ViewGestureController from Cocoa/Mac directory
>+        to UIProcess/, also move some parts of mac/ViewGestreControllerMac.mm to
>+        ViewGestureController.cpp, split up Mac- and iOS-specific parts of
>+        ViewSnapshotStore.cpp into mac/ViewSnapshotMac.mm, then implement 2-finger
>+        touchpad swipe back-forward gesture for GTK based on that.
>+
>+        To avoid name conflict, rename existing ViewGestureController class inside
>+        UIProcess/API/gtk/WebKitWebViewBase.cpp into TouchGestureController.
>+
>+        Since GTK gestures can only work with 3 or 4 fingers, treat horizontal
>+        scrolling events as a swipe as long as there's nowhere to scroll in that
>+        direction and web page doesn't handle the scrolling.
>+
>+        This is only allowed for touchpads, even though it can theoretically work
>+        with touch mice and trackpoints.
>+
>+        The gesture requires every item in back-forward list to have a snapshot.
>+        There's already an existing infrastructure for that, so the patch changes
>+        a bunch of #if PLATFORM(COCOA) statements to also check for GTK platform.
>+        The snapshots have to be taken in sync, so the implementation draws webview
>+        widget into a Cairo image surface.
>+
>+        The gesture is disabled by default, and can be enabled by setting the newly
>+        added 'enable-back-forward-navigation-gestures' property in WebKitSettings to
>+        true.
>+
>+        Gesture drawing is implemented via Cairo. When the gesture is active, the
>+        actual page is drawn into a Cairo group, which is then drawn together with
>+        a given snapshot, as well as dimming and a drop shadow over the "lower" layer.
>+
>+        Also add a memory pressure handler that clears snapshot store when low on memory.
>+
>+        * DerivedSources-input.xcfilelist:
>+        * PlatformGTK.cmake:
>+        * PlatformMac.cmake:
>+        * Shared/SessionState.h: Add snapshot to back-forward items for GTK.
>+        * Shared/WebBackForwardListItem.h: Add snapshot to back-forward items for GTK.
>+        * SourcesCocoa.txt:
>+        * SourcesGTK.txt:
>+        * UIProcess/API/glib/WebKitSettings.cpp:
>+        Added 'enable-back-forward-navigation-gestures' property for enabling the gesture.
>+        (webKitSettingsSetProperty):
>+        (webKitSettingsGetProperty):
>+        (webkit_settings_class_init):
>+        (webkit_settings_get_enable_back_forward_navigation_gestures): Added, GTK only.
>+        (webkit_settings_set_enable_back_forward_navigation_gestures): Added, GTK only.
>+        * UIProcess/API/glib/WebKitWebView.cpp:
>+        (enableBackForwardNavigationGesturesChanged): Added, GTK only.
>+        (webkitWebViewUpdateSettings):
>+        (webkitWebViewDisconnectSettingsSignalHandlers):
>+        * UIProcess/API/gtk/PageClientImpl.cpp:
>+        (WebKit::PageClientImpl::setViewNeedsDisplay): Redraw the whole screen instead of a region during the gesture.
>+        (WebKit::PageClientImpl::takeViewSnapshot): Added.
>+        (WebKit::PageClientImpl::wheelEventWasNotHandledByWebCore): Pass unhandled events to the gesture controller.
>+        (WebKit::PageClientImpl::didRemoveNavigationGestureSnapshot): Redraw the widget immediately after removing snapshot.
>+        (WebKit::PageClientImpl::didStartProvisionalLoadForMainFrame): Added, send a notification to the gesture controller.
>+        (WebKit::PageClientImpl::didFirstVisuallyNonEmptyLayoutForMainFrame):  Send a notification to the gesture controller.
>+        (WebKit::PageClientImpl::didFinishLoadForMainFrame):  Send a notification to the gesture controller.
>+        (WebKit::PageClientImpl::didFailLoadForMainFrame):  Added, send a notification to the gesture controller.
>+        (WebKit::PageClientImpl::didSameDocumentNavigationForMainFrame):  Send a notification to the gesture controller.
>+        (WebKit::PageClientImpl::didRestoreScrollPosition):  Added, send a notification to the gesture controller.
>+        * UIProcess/API/gtk/PageClientImpl.h:
>+        * UIProcess/API/gtk/WebKitSettings.h:
>+        Add webkit_settings_get_enable_back_forward_navigation_gestures() and webkit_settings_get_enable_back_forward_navigation_gestures()
>+        to public API.
>+        * UIProcess/API/gtk/WebKitWebViewBase.cpp:
>+        (webkitWebViewBaseDraw): Pass drawing to ViewGestureController during the gesture.
>+        (webkitWebViewBaseScrollEvent): Pass scroll events to ViewGestureController during the gesture.
>+        (webkitWebViewBaseGestureController): Renamed ViewGestureController to TouchGestureController.
>+        (webkitWebViewBaseViewGestureController): Added.
>+        (webkitWebViewBaseCreateWebPage): Create an instance of ViewGestureController.
>+        (webkitWebViewBaseTakeViewSnapshot): Added.
>+        (webkitWebViewBaseDidStartProvisionalLoadForMainFrame): Added.
>+        (webkitWebViewBaseDidFirstVisuallyNonEmptyLayoutForMainFrame): Added.
>+        (webkitWebViewBaseDidFinishLoadForMainFrame): Added.
>+        (webkitWebViewBaseDidFailLoadForMainFrame): Added.
>+        (webkitWebViewBaseDidSameDocumentNavigationForMainFrame): Added.
>+        (webkitWebViewBaseDidRestoreScrollPosition): Added.
>+        * UIProcess/API/gtk/WebKitWebViewBasePrivate.h:
>+        * UIProcess/API/gtk/docs/webkit2gtk-4.0-sections.txt: Mentioned the added functions in docs.
>+        * UIProcess/Cocoa/WebProcessPoolCocoa.mm:
>+        (WebKit::WebProcessPool::platformInitialize): Move the check from WebMemoryPressureHandlerCocoa.mm here.
>+        * UIProcess/PageClient.h: Add takeViewSnapshot() for GTK.
>+        * UIProcess/ViewGestureController.cpp: Renamed from Source/WebKit/UIProcess/Cocoa/ViewGestureController.cpp.
>+        (WebKit::ViewGestureController::ViewGestureController):
>+        (WebKit::ViewGestureController::~ViewGestureController):
>+        (WebKit::ViewGestureController::disconnectFromProcess):
>+        (WebKit::ViewGestureController::connectToProcess):
>+        (WebKit::ViewGestureController::controllerForGesture):
>+        (WebKit::ViewGestureController::takeNextGestureID):
>+        (WebKit::ViewGestureController::willBeginGesture):
>+        (WebKit::ViewGestureController::didEndGesture):
>+        (WebKit::ViewGestureController::setAlternateBackForwardListSourcePage):
>+        (WebKit::ViewGestureController::canSwipeInDirection const):
>+        (WebKit::ViewGestureController::didStartProvisionalOrSameDocumentLoadForMainFrame):
>+        (WebKit::ViewGestureController::didStartProvisionalLoadForMainFrame):
>+        (WebKit::ViewGestureController::didFirstVisuallyNonEmptyLayoutForMainFrame):
>+        (WebKit::ViewGestureController::didRepaintAfterNavigation):
>+        (WebKit::ViewGestureController::didHitRenderTreeSizeThreshold):
>+        (WebKit::ViewGestureController::didRestoreScrollPosition):
>+        (WebKit::ViewGestureController::didReachMainFrameLoadTerminalState):
>+        (WebKit::ViewGestureController::didSameDocumentNavigationForMainFrame):
>+        (WebKit::ViewGestureController::checkForActiveLoads):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::SnapshotRemovalTracker):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::eventsDescription):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::log const):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::resume):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::start):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::reset):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::stopWaitingForEvent):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::eventOccurred):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::cancelOutstandingEvent):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::hasOutstandingEvent):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackIfPossible):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackImmediately):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::watchdogTimerFired):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::startWatchdog):
>+        (WebKit::deltaShouldCancelSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::PendingSwipeTracker):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanBecomeSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::handleEvent):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::eventWasNotHandledByWebCore):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::tryToStartSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::reset):
>+        (WebKit::ViewGestureController::startSwipeGesture):
>+        (WebKit::ViewGestureController::isPhysicallySwipingLeft const):
>+        (WebKit::ViewGestureController::shouldUseSnapshotForSize):
>+        (WebKit::ViewGestureController::forceRepaintIfNeeded):
>+        (WebKit::ViewGestureController::willEndSwipeGesture):
>+        (WebKit::ViewGestureController::endSwipeGesture):
>+        (WebKit::ViewGestureController::requestRenderTreeSizeNotificationIfNeeded):
>+        * UIProcess/ViewGestureController.h: Renamed from Source/WebKit/UIProcess/Cocoa/ViewGestureController.h.
>+        (WebKit::ViewGestureController::wheelEventWasNotHandledByWebCore):
>+        (WebKit::ViewGestureController::shouldIgnorePinnedState):
>+        (WebKit::ViewGestureController::setShouldIgnorePinnedState):
>+        (WebKit::ViewGestureController::hasActiveMagnificationGesture const):
>+        (WebKit::ViewGestureController::setCustomSwipeViews):
>+        (WebKit::ViewGestureController::setCustomSwipeViewsTopContentInset):
>+        (WebKit::ViewGestureController::setDidMoveSwipeSnapshotCallback):
>+        (WebKit::ViewGestureController::backgroundColorForCurrentSnapshot const):
>+        (WebKit::ViewGestureController::didFinishLoadForMainFrame):
>+        (WebKit::ViewGestureController::didFailLoadForMainFrame):
>+        (WebKit::ViewGestureController::setSwipeGestureEnabled):
>+        (WebKit::ViewGestureController::isSwipeGestureEnabled):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::pause):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::isPaused const):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::hasRemovalCallback const):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::renderTreeSizeThreshold const):
>+        (WebKit::ViewGestureController::SnapshotRemovalTracker::setRenderTreeSizeThreshold):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::shouldIgnorePinnedState):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::setShouldIgnorePinnedState):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::progress const):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::direction const):
>+        * UIProcess/ViewGestureController.messages.in: Renamed from Source/WebKit/UIProcess/Cocoa/ViewGestureController.messages.in.
>+        * UIProcess/ViewSnapshotStore.cpp: Copied from Source/WebKit/UIProcess/mac/ViewSnapshotStore.mm.
>+        (WebKit::ViewSnapshotStore::ViewSnapshotStore):
>+        (WebKit::ViewSnapshotStore::~ViewSnapshotStore):
>+        (WebKit::ViewSnapshotStore::singleton):
>+        (WebKit::ViewSnapshotStore::didAddImageToSnapshot):
>+        (WebKit::ViewSnapshotStore::willRemoveImageFromSnapshot):
>+        (WebKit::ViewSnapshotStore::pruneSnapshots):
>+        (WebKit::ViewSnapshotStore::recordSnapshot):
>+        (WebKit::ViewSnapshotStore::discardSnapshotImages):
>+        (WebKit::ViewSnapshot::~ViewSnapshot):
>+        * UIProcess/ViewSnapshotStore.h: Renamed from Source/WebKit/UIProcess/mac/ViewSnapshotStore.h.
>+        (WebKit::ViewSnapshot::setRenderTreeSize):
>+        (WebKit::ViewSnapshot::renderTreeSize const):
>+        (WebKit::ViewSnapshot::setBackgroundColor):
>+        (WebKit::ViewSnapshot::backgroundColor const):
>+        (WebKit::ViewSnapshot::setViewScrollPosition):
>+        (WebKit::ViewSnapshot::viewScrollPosition const):
>+        (WebKit::ViewSnapshot::setDeviceScaleFactor):
>+        (WebKit::ViewSnapshot::deviceScaleFactor const):
>+        (WebKit::ViewSnapshot::surface const):
>+        (WebKit::ViewSnapshot::imageSizeInBytes const):
>+        (WebKit::ViewSnapshot::size const):
>+        (WebKit::ViewSnapshotStore::setDisableSnapshotVolatilityForTesting):
>+        (WebKit::ViewSnapshotStore::disableSnapshotVolatilityForTesting const):
>+        * UIProcess/WebBackForwardList.cpp:
>+        (WebKit::WebBackForwardList::didRemoveItem): Unset snapshot for GTK.
>+        * UIProcess/WebMemoryPressureHandler.cpp: Copied from Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm.
>+        (WebKit::installMemoryPressureHandler):
>+        * UIProcess/WebMemoryPressureHandler.h: Renamed from Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.h.
>+        * UIProcess/WebPageProxy.cpp:
>+        (WebKit::WebPageProxy::recordNavigationSnapshot): Take snapshots for GTK.
>+        * UIProcess/WebPageProxy.h:
>+        * UIProcess/gtk/ViewGestureControllerGtk.cpp: Added. This is a port of
>+        UIProcess/mac/ViewGestureControllerMac.mm. SwipeProgressTracker class is a
>+        re-implementation of trackSwipeEventWithOptions.
>+        (WebKit::isEventStop):
>+        (WebKit::ViewGestureController::platformTeardown):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanStartSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanEndSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanInfluenceSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventGetScrollingDeltas):
>+        (WebKit::ViewGestureController::handleScrollWheelEvent):
>+        (WebKit::ViewGestureController::trackSwipeGesture):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::SwipeProgressTracker):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::startTracking):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::reset):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::handleEvent):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::startAnimation):
>+        (WebKit::easeOutCubic):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::onAnimationTick):
>+        (WebKit::ViewGestureController::SwipeProgressTracker::endAnimation):
>+        (WebKit::ViewGestureController::beginSwipeGesture):
>+        (WebKit::ViewGestureController::handleSwipeGesture):
>+        (WebKit::ViewGestureController::draw):
>+        (WebKit::ViewGestureController::removeSwipeSnapshot):
>+        (WebKit::ViewGestureController::beginSimulatedSwipeInDirectionForTesting):
>+        (WebKit::ViewGestureController::completeSimulatedSwipeInDirectionForTesting):
>+        * UIProcess/gtk/ViewSnapshotStoreGtk.cpp: Renamed from Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm.
>+        (WebKit::ViewSnapshot::create):
>+        (WebKit::ViewSnapshot::ViewSnapshot):
>+        (WebKit::ViewSnapshot::hasImage const):
>+        (WebKit::ViewSnapshot::clearImage):
>+        (WebKit::ViewSnapshot::imageSizeInBytes const):
>+        (WebKit::ViewSnapshot::size const):
>+        * UIProcess/gtk/WebProcessPoolGtk.cpp:
>+        (WebKit::memoryPressureMonitorDisabled): Added.
>+        (WebKit::WebProcessPool::platformInitialize): Install memory pressure handler.
>+        (WebKit::WebProcessPool::platformInitializeWebProcess): Use memoryPressureMonitorDisabled().
>+        * UIProcess/mac/ViewGestureControllerMac.mm:
>+        Moved many functions into UIProcess/ViewGestureController.cpp
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanStartSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanEndSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanInfluenceSwipe):
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventGetScrollingDeltas):
>+        (WebKit::ViewGestureController::trackSwipeGesture):
>+        (WebKit::scrollEventCanInfluenceSwipe): Deleted.
>+        (WebKit::deltaShouldCancelSwipe): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::PendingSwipeTracker): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::scrollEventCanBecomeSwipe): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::handleEvent): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::eventWasNotHandledByWebCore): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::tryToStartSwipe): Deleted.
>+        (WebKit::ViewGestureController::PendingSwipeTracker::reset): Deleted.
>+        (WebKit::ViewGestureController::willEndSwipeGesture): Deleted.
>+        (WebKit::ViewGestureController::shouldUseSnapshotForSize): Deleted.
>+        (WebKit::ViewGestureController::isPhysicallySwipingLeft const): Deleted.
>+        (WebKit::ViewGestureController::endSwipeGesture): Deleted.
>+        (WebKit::ViewGestureController::forceRepaintIfNeeded): Deleted.
>+        (WebKit::ViewGestureController::requestRenderTreeSizeNotificationIfNeeded): Deleted.
>+        * UIProcess/mac/ViewSnapshotStoreMac.mm: Renamed from Source/WebKit/UIProcess/mac/ViewSnapshotStore.mm.
>+        (WebKit::ViewSnapshotStore::snapshottingContext):
>+        (WebKit::ViewSnapshot::create):
>+        (WebKit::ViewSnapshot::ViewSnapshot):
>+        (WebKit::ViewSnapshot::setSurface):
>+        (WebKit::ViewSnapshot::hasImage const):
>+        (WebKit::ViewSnapshot::clearImage):
>+        (WebKit::ViewSnapshot::setVolatile):
>+        (WebKit::ViewSnapshot::asLayerContents):
>+        (WebKit::ViewSnapshot::asImageForTesting):
>+        * WebKit.xcodeproj/project.pbxproj:
>+        * WebProcess/WebPage/ViewGestureGeometryCollector.cpp:
>+        Make SetRenderTreeSizeNotificationThreshold() cross-platform.
>+        (WebKit::ViewGestureGeometryCollector::ViewGestureGeometryCollector):
>+        (WebKit::ViewGestureGeometryCollector::computeMinimumAndMaximumViewportScales const):
>+        (WebKit::ViewGestureGeometryCollector::mainFrameDidLayout):
>+        * WebProcess/WebPage/ViewGestureGeometryCollector.h:
>+        * WebProcess/WebPage/ViewGestureGeometryCollector.messages.in:
>+        * WebProcess/WebPage/WebPage.cpp:
>+        Start using ViewGestureGeometryCollector for GTK.
>+        (WebKit::WebPage::mainFrameDidLayout):
>+        * WebProcess/WebPage/WebPage.h:
>+
> 2019-02-08  Alex Christensen  <achristensen@webkit.org>
> 
>         Add SPI to use networking daemon instead of XPC service
>diff --git a/Source/WebKit/DerivedSources-input.xcfilelist b/Source/WebKit/DerivedSources-input.xcfilelist
>index 586977c902d00c89bd90c2e161f39c290a0d249e..517f3ed5cfa1d5e89bcc4dd02301a86b3db495fe 100644
>--- a/Source/WebKit/DerivedSources-input.xcfilelist
>+++ b/Source/WebKit/DerivedSources-input.xcfilelist
>@@ -63,7 +63,6 @@ $(PROJECT_DIR)/UIProcess/Automation/WebAutomationSession.messages.in
> $(PROJECT_DIR)/UIProcess/Cocoa/PlaybackSessionManagerProxy.messages.in
> $(PROJECT_DIR)/UIProcess/Cocoa/UserMediaCaptureManagerProxy.messages.in
> $(PROJECT_DIR)/UIProcess/Cocoa/VideoFullscreenManagerProxy.messages.in
>-$(PROJECT_DIR)/UIProcess/Cocoa/ViewGestureController.messages.in
> $(PROJECT_DIR)/UIProcess/Downloads/DownloadProxy.messages.in
> $(PROJECT_DIR)/UIProcess/DrawingAreaProxy.messages.in
> $(PROJECT_DIR)/UIProcess/Network/CustomProtocols/LegacyCustomProtocolManagerProxy.messages.in
>@@ -72,6 +71,7 @@ $(PROJECT_DIR)/UIProcess/Plugins/PluginProcessProxy.messages.in
> $(PROJECT_DIR)/UIProcess/RemoteLayerTree/RemoteLayerTreeDrawingAreaProxy.messages.in
> $(PROJECT_DIR)/UIProcess/RemoteWebInspectorProxy.messages.in
> $(PROJECT_DIR)/UIProcess/UserContent/WebUserContentControllerProxy.messages.in
>+$(PROJECT_DIR)/UIProcess/ViewGestureController.messages.in
> $(PROJECT_DIR)/UIProcess/VisitedLinkStore.messages.in
> $(PROJECT_DIR)/UIProcess/WebAuthentication/WebAuthenticatorCoordinatorProxy.messages.in
> $(PROJECT_DIR)/UIProcess/WebCookieManagerProxy.messages.in
>diff --git a/Source/WebKit/PlatformGTK.cmake b/Source/WebKit/PlatformGTK.cmake
>index 3f53c1639bb4b37276314736113a441960617626..634b0003d951e14879de2309977c763a8c4bda85 100644
>--- a/Source/WebKit/PlatformGTK.cmake
>+++ b/Source/WebKit/PlatformGTK.cmake
>@@ -35,7 +35,11 @@ list(APPEND WebKit_UNIFIED_SOURCE_LIST_FILES
> list(APPEND WebKit_MESSAGES_IN_FILES
>     NetworkProcess/CustomProtocols/LegacyCustomProtocolManager.messages.in
> 
>+    UIProcess/ViewGestureController.messages.in
>+
>     UIProcess/Network/CustomProtocols/LegacyCustomProtocolManagerProxy.messages.in
>+
>+    WebProcess/WebPage/ViewGestureGeometryCollector.messages.in
> )
> 
> list(APPEND WebKit_DERIVED_SOURCES
>diff --git a/Source/WebKit/PlatformMac.cmake b/Source/WebKit/PlatformMac.cmake
>index a6cfe1de86edec09da5ed95c9a7397a81d85ae7b..19362b2984297a379929236b12e0274a178fe511 100644
>--- a/Source/WebKit/PlatformMac.cmake
>+++ b/Source/WebKit/PlatformMac.cmake
>@@ -161,6 +161,8 @@ list(APPEND WebKit_SOURCES
> 
>     UIProcess/HighPerformanceGraphicsUsageSampler.cpp
>     UIProcess/PerActivityStateCPUUsageSampler.cpp
>+    UIProcess/ViewGestureController.cpp
>+    UIProcess/ViewSnapshotStore.cpp
> 
>     UIProcess/Automation/WebAutomationSession.cpp
> 
>@@ -253,7 +255,6 @@ list(APPEND WebKit_SOURCES
>     UIProcess/Cocoa/SessionStateCoding.mm
>     UIProcess/Cocoa/UIDelegate.mm
>     UIProcess/Cocoa/VersionChecks.mm
>-    UIProcess/Cocoa/ViewGestureController.cpp
>     UIProcess/Cocoa/WKFullKeyboardAccessWatcher.mm
>     UIProcess/Cocoa/WKReloadFrameErrorRecoveryAttempter.mm
>     UIProcess/Cocoa/WKWebViewContentProviderRegistry.mm
>@@ -291,7 +292,7 @@ list(APPEND WebKit_SOURCES
>     UIProcess/mac/TextCheckerMac.mm
>     UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.mm
>     UIProcess/mac/ViewGestureControllerMac.mm
>-    UIProcess/mac/ViewSnapshotStore.mm
>+    UIProcess/mac/ViewSnapshotStoreMac.mm
>     UIProcess/mac/WKFullScreenWindowController.mm
>     UIProcess/mac/WKImmediateActionController.mm
>     UIProcess/mac/WKInspectorViewController.mm
>@@ -466,8 +467,9 @@ list(APPEND WebKit_MESSAGES_IN_FILES
> 
>     Shared/API/Cocoa/RemoteObjectRegistry.messages.in
> 
>+    UIProcess/ViewGestureController.messages.in
>+
>     UIProcess/Cocoa/VideoFullscreenManagerProxy.messages.in
>-    UIProcess/Cocoa/ViewGestureController.messages.in
> 
>     UIProcess/Network/CustomProtocols/LegacyCustomProtocolManagerProxy.messages.in
> 
>diff --git a/Source/WebKit/Shared/SessionState.h b/Source/WebKit/Shared/SessionState.h
>index d26791da99c36d284ff2e7d50ce082678d0f08b0..69b9955de77ec98b64d4a752d17862df2ba60384 100644
>--- a/Source/WebKit/Shared/SessionState.h
>+++ b/Source/WebKit/Shared/SessionState.h
>@@ -25,10 +25,7 @@
> 
> #pragma once
> 
>-#if PLATFORM(COCOA)
> #include "ViewSnapshotStore.h"
>-#endif
>-
> #include <WebCore/BackForwardItemIdentifier.h>
> #include <WebCore/FloatRect.h>
> #include <WebCore/FrameLoaderTypes.h>
>@@ -133,7 +130,7 @@ struct BackForwardListItemState {
>     WebCore::BackForwardItemIdentifier identifier;
> 
>     PageState pageState;
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     RefPtr<ViewSnapshot> snapshot;
> #endif
> };
>diff --git a/Source/WebKit/Shared/WebBackForwardListItem.h b/Source/WebKit/Shared/WebBackForwardListItem.h
>index aaf6514e7a67c36187b11f99d7ad4e7d03efd4f2..bff0c882041f6a9aa8332166fd7b377ec3f1b583 100644
>--- a/Source/WebKit/Shared/WebBackForwardListItem.h
>+++ b/Source/WebKit/Shared/WebBackForwardListItem.h
>@@ -66,7 +66,7 @@ public:
>     bool itemIsInSameDocument(const WebBackForwardListItem&) const;
>     bool itemIsClone(const WebBackForwardListItem&);
> 
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     ViewSnapshot* snapshot() const { return m_itemState.snapshot.get(); }
>     void setSnapshot(RefPtr<ViewSnapshot>&& snapshot) { m_itemState.snapshot = WTFMove(snapshot); }
> #endif
>diff --git a/Source/WebKit/SourcesCocoa.txt b/Source/WebKit/SourcesCocoa.txt
>index 2f5c087b7a8eb4a085a30326f0dd84b80fed4bc9..5f6b3f0b3ab785a39c295a407d50292a255dd08e 100644
>--- a/Source/WebKit/SourcesCocoa.txt
>+++ b/Source/WebKit/SourcesCocoa.txt
>@@ -205,9 +205,12 @@ UIProcess/_WKWebViewPrintFormatter.mm
> UIProcess/ApplicationStateTracker.mm
> UIProcess/HighPerformanceGraphicsUsageSampler.cpp
> UIProcess/PerActivityStateCPUUsageSampler.cpp
>+UIProcess/ViewGestureController.cpp
>+UIProcess/ViewSnapshotStore.cpp @no-unify
> UIProcess/WebDataListSuggestionsDropdown.cpp
> UIProcess/WebMediaSessionFocusManager.cpp
> UIProcess/WebMediaSessionFocusManagerClient.cpp
>+UIProcess/WebMemoryPressureHandler.cpp
> UIProcess/WKImagePreviewViewController.mm
> UIProcess/WKInspectorHighlightView.mm
> 
>@@ -338,8 +341,6 @@ UIProcess/Cocoa/UIDelegate.mm
> UIProcess/Cocoa/UserMediaCaptureManagerProxy.cpp
> UIProcess/Cocoa/VersionChecks.mm
> UIProcess/Cocoa/VideoFullscreenManagerProxy.mm
>-UIProcess/Cocoa/ViewGestureController.cpp
>-UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm
> UIProcess/Cocoa/WebPageProxyCocoa.mm
> UIProcess/Cocoa/WebPasteboardProxyCocoa.mm
> UIProcess/Cocoa/WebProcessPoolCocoa.mm
>@@ -426,7 +427,7 @@ UIProcess/mac/ServicesController.mm
> UIProcess/mac/TextCheckerMac.mm
> UIProcess/mac/TiledCoreAnimationDrawingAreaProxy.mm
> UIProcess/mac/ViewGestureControllerMac.mm
>-UIProcess/mac/ViewSnapshotStore.mm
>+UIProcess/mac/ViewSnapshotStoreMac.mm
> UIProcess/mac/WebColorPickerMac.mm
> UIProcess/mac/WebContextMenuProxyMac.mm
> UIProcess/mac/WebCookieManagerProxyMac.mm
>diff --git a/Source/WebKit/SourcesGTK.txt b/Source/WebKit/SourcesGTK.txt
>index ca925bc290acef12de90c7842e155393f30d6a74..15ae6b5d72ef92d3e29ee8bea730c043c5a076cf 100644
>--- a/Source/WebKit/SourcesGTK.txt
>+++ b/Source/WebKit/SourcesGTK.txt
>@@ -112,7 +112,10 @@ UIProcess/BackingStore.cpp
> UIProcess/DefaultUndoController.cpp
> UIProcess/DrawingAreaProxyImpl.cpp
> UIProcess/LegacySessionStateCodingNone.cpp
>+UIProcess/ViewGestureController.cpp
>+UIProcess/ViewSnapshotStore.cpp @no-unify
> UIProcess/WebGrammarDetail.cpp
>+UIProcess/WebMemoryPressureHandler.cpp @no-unify
> UIProcess/WebTextChecker.cpp
> UIProcess/WebTextCheckerClient.cpp
> UIProcess/WebViewportAttributes.cpp
>@@ -240,6 +243,8 @@ UIProcess/gtk/InputMethodFilter.cpp @no-unify
> UIProcess/gtk/KeyBindingTranslator.cpp
> UIProcess/gtk/RemoteWebInspectorProxyGtk.cpp @no-unify
> UIProcess/gtk/TextCheckerGtk.cpp @no-unify
>+UIProcess/gtk/ViewGestureControllerGtk.cpp @no-unify
>+UIProcess/gtk/ViewSnapshotStoreGtk.cpp @no-unify
> UIProcess/gtk/WaylandCompositor.cpp @no-unify
> UIProcess/gtk/WebColorPickerGtk.cpp @no-unify
> UIProcess/gtk/WebContextMenuProxyGtk.cpp
>@@ -397,6 +402,7 @@ WebProcess/WebCoreSupport/soup/WebFrameNetworkingContext.cpp
> WebProcess/WebPage/AcceleratedDrawingArea.cpp
> WebProcess/WebPage/AcceleratedSurface.cpp
> WebProcess/WebPage/LayerTreeHost.cpp
>+WebProcess/WebPage/ViewGestureGeometryCollector.cpp
> 
> WebProcess/WebPage/CoordinatedGraphics/CompositingCoordinator.cpp
> WebProcess/WebPage/CoordinatedGraphics/CoordinatedLayerTreeHost.cpp
>diff --git a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
>index 5e14b616f682f65db05f03a01d4ec8e3b606f7e8..d2b86c31e94d99d4a1e6cc529ae4ecec6f9b223c 100644
>--- a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
>+++ b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
>@@ -381,7 +381,7 @@ void WKWebsiteDataStoreSetStatisticsPruneEntriesDownTo(WKWebsiteDataStoreRef dat
> void WKWebsiteDataStoreStatisticsClearInMemoryAndPersistentStore(WKWebsiteDataStoreRef dataStoreRef, void* context, WKWebsiteDataStoreStatisticsClearInMemoryAndPersistentStoreFunction callback)
> {
> #if ENABLE(RESOURCE_LOAD_STATISTICS)
>-    WebKit::toImpl(dataStoreRef)->websiteDataStore().scheduleClearInMemoryAndPersistent(ShouldGrandfatherStatistics::Yes, [context, callback]() {
>+    WebKit::toImpl(dataStoreRef)->websiteDataStore().scheduleClearInMemoryAndPersistent(WebKit::ShouldGrandfatherStatistics::Yes, [context, callback]() {
>         callback(context);
>     });
> #else
>@@ -392,7 +392,7 @@ void WKWebsiteDataStoreStatisticsClearInMemoryAndPersistentStore(WKWebsiteDataSt
> void WKWebsiteDataStoreStatisticsClearInMemoryAndPersistentStoreModifiedSinceHours(WKWebsiteDataStoreRef dataStoreRef, unsigned hours, void* context, WKWebsiteDataStoreStatisticsClearInMemoryAndPersistentStoreModifiedSinceHoursFunction callback)
> {
> #if ENABLE(RESOURCE_LOAD_STATISTICS)
>-    WebKit::toImpl(dataStoreRef)->websiteDataStore().scheduleClearInMemoryAndPersistent(WallTime::now() - Seconds::fromHours(hours), ShouldGrandfatherStatistics::Yes, [context, callback]() {
>+    WebKit::toImpl(dataStoreRef)->websiteDataStore().scheduleClearInMemoryAndPersistent(WallTime::now() - Seconds::fromHours(hours), WebKit::ShouldGrandfatherStatistics::Yes, [context, callback]() {
>         callback(context);
>     });
> #else
>@@ -430,7 +430,7 @@ void WKWebsiteDataStoreStatisticsResetToConsistentState(WKWebsiteDataStoreRef da
>     store.clearResourceLoadStatisticsInWebProcesses([callbackAggregator = callbackAggregator.copyRef()] { });
>     store.resetCacheMaxAgeCapForPrevalentResources([callbackAggregator = callbackAggregator.copyRef()] { });
>     store.resetParametersToDefaultValues([callbackAggregator = callbackAggregator.copyRef()] { });
>-    store.scheduleClearInMemoryAndPersistent(ShouldGrandfatherStatistics::No, [callbackAggregator = callbackAggregator.copyRef()] { });
>+    store.scheduleClearInMemoryAndPersistent(WebKit::ShouldGrandfatherStatistics::No, [callbackAggregator = callbackAggregator.copyRef()] { });
> #else
>     UNUSED_PARAM(dataStoreRef);
>     completionHandler(context);
>diff --git a/Source/WebKit/UIProcess/API/glib/WebKitSettings.cpp b/Source/WebKit/UIProcess/API/glib/WebKitSettings.cpp
>index 4ec7f98139a071fcbd1682a2066d90a7a9f4a712..a840651c6daa81c1b5fa6bed5e03319020295ec4 100644
>--- a/Source/WebKit/UIProcess/API/glib/WebKitSettings.cpp
>+++ b/Source/WebKit/UIProcess/API/glib/WebKitSettings.cpp
>@@ -80,6 +80,9 @@ struct _WebKitSettingsPrivate {
>     bool allowModalDialogs { false };
>     bool zoomTextOnly { false };
>     double screenDpi { 96 };
>+#if PLATFORM(GTK)
>+    bool enableBackForwardNavigationGestures { false };
>+#endif
> };
> 
> /**
>@@ -161,6 +164,7 @@ enum {
>     PROP_ALLOW_UNIVERSAL_ACCESS_FROM_FILE_URLS,
> #if PLATFORM(GTK)
>     PROP_HARDWARE_ACCELERATION_POLICY,
>+    PROP_ENABLE_BACK_FORWARD_NAVIGATION_GESTURES,
> #endif
> };
> 
>@@ -381,6 +385,9 @@ static void webKitSettingsSetProperty(GObject* object, guint propId, const GValu
>     case PROP_HARDWARE_ACCELERATION_POLICY:
>         webkit_settings_set_hardware_acceleration_policy(settings, static_cast<WebKitHardwareAccelerationPolicy>(g_value_get_enum(value)));
>         break;
>+    case PROP_ENABLE_BACK_FORWARD_NAVIGATION_GESTURES:
>+        webkit_settings_set_enable_back_forward_navigation_gestures(settings, g_value_get_boolean(value));
>+        break;
> #endif
>     default:
>         G_OBJECT_WARN_INVALID_PROPERTY_ID(object, propId, paramSpec);
>@@ -560,6 +567,9 @@ static void webKitSettingsGetProperty(GObject* object, guint propId, GValue* val
>     case PROP_HARDWARE_ACCELERATION_POLICY:
>         g_value_set_enum(value, webkit_settings_get_hardware_acceleration_policy(settings));
>         break;
>+    case PROP_ENABLE_BACK_FORWARD_NAVIGATION_GESTURES:
>+        g_value_set_boolean(value, webkit_settings_get_enable_back_forward_navigation_gestures(settings));
>+        break;
> #endif
>     default:
>         G_OBJECT_WARN_INVALID_PROPERTY_ID(object, propId, paramSpec);
>@@ -1443,6 +1453,21 @@ static void webkit_settings_class_init(WebKitSettingsClass* klass)
>             WEBKIT_TYPE_HARDWARE_ACCELERATION_POLICY,
>             WEBKIT_HARDWARE_ACCELERATION_POLICY_ON_DEMAND,
>             readWriteConstructParamFlags));
>+
>+    /**
>+     * WebKitSettings:enable-back-forward-navigation-gestures:
>+     *
>+     * Enable or disable horizontal swipe gesture for back-forward navigation.
>+     *
>+     * Since: 2.24
>+     */
>+    g_object_class_install_property(gObjectClass,
>+        PROP_ENABLE_BACK_FORWARD_NAVIGATION_GESTURES,
>+        g_param_spec_boolean("enable-back-forward-navigation-gestures",
>+            _("Enable back-forward navigation gestures"),
>+            _("Whether horizontal swipe gesture will trigger back-forward navigation"),
>+            FALSE,
>+            readWriteConstructParamFlags));
> #endif // PLATFOTM(GTK)
> }
> 
>@@ -3512,6 +3537,44 @@ void webkit_settings_set_hardware_acceleration_policy(WebKitSettings* settings,
>         g_object_notify(G_OBJECT(settings), "hardware-acceleration-policy");
> }
> 
>+/**
>+ * webkit_settings_get_enable_back_forward_navigation_gestures:
>+ * @settings: a #WebKitSettings
>+ *
>+ * Get the #WebKitSettings:enable-back-forward-navigation-gestures property.
>+ *
>+ * Returns: %TRUE if horizontal swipe gesture will trigger back-forward navigaiton or %FALSE otherwise.
>+ *
>+ * Since: 2.24
>+ */
>+gboolean webkit_settings_get_enable_back_forward_navigation_gestures(WebKitSettings* settings)
>+{
>+    g_return_val_if_fail(WEBKIT_IS_SETTINGS(settings), FALSE);
>+
>+    return settings->priv->enableBackForwardNavigationGestures;
>+}
>+
>+/**
>+ * webkit_settings_set_enable_back_forward_navigation_gestures:
>+ * @settings: a #WebKitSettings
>+ * @enableed: value to be set
>+ *
>+ * Set the #WebKitSettings:enable-back-forward-navigation-gestures property.
>+ *
>+ * Since: 2.24
>+ */
>+void webkit_settings_set_enable_back_forward_navigation_gestures(WebKitSettings* settings, gboolean enableed)
>+{
>+    g_return_if_fail(WEBKIT_IS_SETTINGS(settings));
>+
>+    WebKitSettingsPrivate* priv = settings->priv;
>+    if (priv->enableBackForwardNavigationGestures == enableed)
>+        return;
>+
>+    priv->enableBackForwardNavigationGestures = enableed;
>+    g_object_notify(G_OBJECT(settings), "enable-back-forward-navigation-gestures");
>+}
>+
> /**
>  * webkit_settings_font_size_to_points:
>  * @pixels: the font size in pixels to convert to points
>diff --git a/Source/WebKit/UIProcess/API/glib/WebKitWebView.cpp b/Source/WebKit/UIProcess/API/glib/WebKitWebView.cpp
>index fafc8036c7bb49da1f30b6723576c9d0cab0cb54..e413fba3e474af7d24d8c460b2e167bb108fcec9 100644
>--- a/Source/WebKit/UIProcess/API/glib/WebKitWebView.cpp
>+++ b/Source/WebKit/UIProcess/API/glib/WebKitWebView.cpp
>@@ -501,6 +501,16 @@ static void userAgentChanged(WebKitSettings* settings, GParamSpec*, WebKitWebVie
> }
> 
> #if PLATFORM(GTK)
>+static void enableBackForwardNavigationGesturesChanged(WebKitSettings* settings, GParamSpec*, WebKitWebView* webView)
>+{
>+    gboolean enable = webkit_settings_get_enable_back_forward_navigation_gestures(settings);
>+
>+    ViewGestureController& controller = webkitWebViewBaseViewGestureController(WEBKIT_WEB_VIEW_BASE(webView));
>+    controller.setSwipeGestureEnabled(enable);
>+
>+    getPage(webView).setShouldRecordNavigationSnapshots(enable);
>+}
>+
> static void webkitWebViewUpdateFavicon(WebKitWebView* webView, cairo_surface_t* favicon)
> {
>     WebKitWebViewPrivate* priv = webView->priv;
>@@ -581,10 +591,16 @@ static void webkitWebViewUpdateSettings(WebKitWebView* webView)
>     page.setPreferences(*webkitSettingsGetPreferences(settings));
>     page.setCanRunModal(webkit_settings_get_allow_modal_dialogs(settings));
>     page.setCustomUserAgent(String::fromUTF8(webkit_settings_get_user_agent(settings)));
>+#if PLATFORM(GTK)
>+    enableBackForwardNavigationGesturesChanged(settings, nullptr, webView);
>+#endif
> 
>     g_signal_connect(settings, "notify::allow-modal-dialogs", G_CALLBACK(allowModalDialogsChanged), webView);
>     g_signal_connect(settings, "notify::zoom-text-only", G_CALLBACK(zoomTextOnlyChanged), webView);
>     g_signal_connect(settings, "notify::user-agent", G_CALLBACK(userAgentChanged), webView);
>+#if PLATFORM(GTK)
>+    g_signal_connect(settings, "notify::enable-back-forward-navigation-gestures", G_CALLBACK(enableBackForwardNavigationGesturesChanged), webView);
>+#endif
> }
> 
> static void webkitWebViewDisconnectSettingsSignalHandlers(WebKitWebView* webView)
>@@ -596,6 +612,9 @@ static void webkitWebViewDisconnectSettingsSignalHandlers(WebKitWebView* webView
>     g_signal_handlers_disconnect_by_func(settings, reinterpret_cast<gpointer>(allowModalDialogsChanged), webView);
>     g_signal_handlers_disconnect_by_func(settings, reinterpret_cast<gpointer>(zoomTextOnlyChanged), webView);
>     g_signal_handlers_disconnect_by_func(settings, reinterpret_cast<gpointer>(userAgentChanged), webView);
>+#if PLATFORM(GTK)
>+    g_signal_handlers_disconnect_by_func(settings, reinterpret_cast<gpointer>(enableBackForwardNavigationGesturesChanged), webView);
>+#endif
> }
> 
> #if PLATFORM(GTK)
>diff --git a/Source/WebKit/UIProcess/API/gtk/PageClientImpl.cpp b/Source/WebKit/UIProcess/API/gtk/PageClientImpl.cpp
>index 317859d75335e7ddca0307204dcce5e4de1e012e..4c734e31d5b12b113b206f2f452ae294468e6079 100644
>--- a/Source/WebKit/UIProcess/API/gtk/PageClientImpl.cpp
>+++ b/Source/WebKit/UIProcess/API/gtk/PageClientImpl.cpp
>@@ -32,6 +32,7 @@
> #include "NativeWebKeyboardEvent.h"
> #include "NativeWebMouseEvent.h"
> #include "NativeWebWheelEvent.h"
>+#include "ViewSnapshotStore.h"
> #include "WebColorPickerGtk.h"
> #include "WebContextMenuProxyGtk.h"
> #include "WebEventFactory.h"
>@@ -67,6 +68,16 @@ std::unique_ptr<DrawingAreaProxy> PageClientImpl::createDrawingAreaProxy(WebProc
> 
> void PageClientImpl::setViewNeedsDisplay(const WebCore::Region& region)
> {
>+    WebPageProxy* pageProxy = webkitWebViewBaseGetPage(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>+    ASSERT(pageProxy);
>+
>+    // During the gesture, the page may be displayed with an offset.
>+    // To avoid visual glitches, redraw the whole page.
>+    if (pageProxy->isShowingNavigationGestureSnapshot()) {
>+        gtk_widget_queue_draw(m_viewWidget);
>+        return;
>+    }
>+
>     gtk_widget_queue_draw_region(m_viewWidget, toCairoRegion(region).get());
> }
> 
>@@ -255,6 +266,11 @@ void PageClientImpl::selectionDidChange()
>         webkitWebViewSelectionDidChange(WEBKIT_WEB_VIEW(m_viewWidget));
> }
> 
>+RefPtr<ViewSnapshot> PageClientImpl::takeViewSnapshot()
>+{
>+    return webkitWebViewBaseTakeViewSnapshot(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>+}
>+
> void PageClientImpl::didChangeContentSize(const IntSize& size)
> {
>     webkitWebViewBaseSetContentsSize(WEBKIT_WEB_VIEW_BASE(m_viewWidget), size);
>@@ -404,6 +420,12 @@ void PageClientImpl::doneWithTouchEvent(const NativeWebTouchEvent& event, bool w
> 
> void PageClientImpl::wheelEventWasNotHandledByWebCore(const NativeWebWheelEvent& event)
> {
>+    ViewGestureController& controller = webkitWebViewBaseViewGestureController(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>+    if (controller.isSwipeGestureEnabled()) {
>+        controller.wheelEventWasNotHandledByWebCore(&event.nativeEvent()->scroll);
>+        return;
>+    }
>+
>     webkitWebViewBaseForwardNextWheelEvent(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>     gtk_main_do_event(event.nativeEvent());
> }
>@@ -434,18 +456,37 @@ void PageClientImpl::willRecordNavigationSnapshot(WebBackForwardListItem&)
> 
> void PageClientImpl::didRemoveNavigationGestureSnapshot()
> {
>+    gtk_widget_queue_draw(m_viewWidget);
>+}
>+
>+void PageClientImpl::didStartProvisionalLoadForMainFrame()
>+{
>+    webkitWebViewBaseDidStartProvisionalLoadForMainFrame(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
> }
> 
> void PageClientImpl::didFirstVisuallyNonEmptyLayoutForMainFrame()
> {
>+    webkitWebViewBaseDidFirstVisuallyNonEmptyLayoutForMainFrame(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
> }
> 
> void PageClientImpl::didFinishLoadForMainFrame()
> {
>+    webkitWebViewBaseDidFinishLoadForMainFrame(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>+}
>+
>+void PageClientImpl::didFailLoadForMainFrame()
>+{
>+    webkitWebViewBaseDidFailLoadForMainFrame(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
>+}
>+
>+void PageClientImpl::didSameDocumentNavigationForMainFrame(SameDocumentNavigationType type)
>+{
>+    webkitWebViewBaseDidSameDocumentNavigationForMainFrame(WEBKIT_WEB_VIEW_BASE(m_viewWidget), type);
> }
> 
>-void PageClientImpl::didSameDocumentNavigationForMainFrame(SameDocumentNavigationType)
>+void PageClientImpl::didRestoreScrollPosition()
> {
>+    webkitWebViewBaseDidRestoreScrollPosition(WEBKIT_WEB_VIEW_BASE(m_viewWidget));
> }
> 
> void PageClientImpl::didChangeBackgroundColor()
>diff --git a/Source/WebKit/UIProcess/API/gtk/PageClientImpl.h b/Source/WebKit/UIProcess/API/gtk/PageClientImpl.h
>index d27842e734329b4dea7c8d71e397d32b721b4686..93ca18f59f22d35c91663097b07b78590fefc092 100644
>--- a/Source/WebKit/UIProcess/API/gtk/PageClientImpl.h
>+++ b/Source/WebKit/UIProcess/API/gtk/PageClientImpl.h
>@@ -88,6 +88,7 @@ private:
>     RefPtr<WebColorPicker> createColorPicker(WebPageProxy*, const WebCore::Color& initialColor, const WebCore::IntRect&, Vector<WebCore::Color>&&) override;
> #endif
>     void selectionDidChange() override;
>+    RefPtr<ViewSnapshot> takeViewSnapshot() override;
> #if ENABLE(DRAG_SUPPORT)
>     void startDrag(Ref<WebCore::SelectionData>&&, WebCore::DragOperation, RefPtr<ShareableBitmap>&& dragImage) override;
> #endif
>@@ -99,7 +100,7 @@ private:
>     void handleDownloadRequest(DownloadProxy*) override;
>     void didChangeContentSize(const WebCore::IntSize&) override;
>     void didCommitLoadForMainFrame(const String& mimeType, bool useCustomContentProvider) override;
>-    void didFailLoadForMainFrame() override { }
>+    void didFailLoadForMainFrame() override;
> 
>     // Auxiliary Client Creation
> #if ENABLE(FULLSCREEN_API)
>@@ -125,6 +126,7 @@ private:
>     void willRecordNavigationSnapshot(WebBackForwardListItem&) override;
>     void didRemoveNavigationGestureSnapshot() override;
> 
>+    void didStartProvisionalLoadForMainFrame() override;
>     void didFirstVisuallyNonEmptyLayoutForMainFrame() override;
>     void didFinishLoadForMainFrame() override;
>     void didSameDocumentNavigationForMainFrame(SameDocumentNavigationType) override;
>@@ -140,7 +142,7 @@ private:
>     void refView() override;
>     void derefView() override;
> 
>-    void didRestoreScrollPosition() override { }
>+    void didRestoreScrollPosition() override;
>     void isPlayingAudioWillChange() final { }
>     void isPlayingAudioDidChange() final { }
> 
>diff --git a/Source/WebKit/UIProcess/API/gtk/WebKitSettings.h b/Source/WebKit/UIProcess/API/gtk/WebKitSettings.h
>index cb2c206e2f6879d7377e209538c56ce5b03ab391..ff203373d8dc1e086587e4067d7ce4f2013daf5a 100644
>--- a/Source/WebKit/UIProcess/API/gtk/WebKitSettings.h
>+++ b/Source/WebKit/UIProcess/API/gtk/WebKitSettings.h
>@@ -472,6 +472,13 @@ WEBKIT_API void
> webkit_settings_set_hardware_acceleration_policy               (WebKitSettings *settings,
>                                                                 WebKitHardwareAccelerationPolicy policy);
> 
>+WEBKIT_API gboolean
>+webkit_settings_get_enable_back_forward_navigation_gestures    (WebKitSettings *settings);
>+
>+WEBKIT_API void
>+webkit_settings_set_enable_back_forward_navigation_gestures    (WebKitSettings *settings,
>+                                                                gboolean        enableed);
>+
> WEBKIT_API guint32
> webkit_settings_font_size_to_points                            (guint32 pixels);
> 
>diff --git a/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp b/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp
>index c3cc9eab582d326b3fa383964292f80230bd7b6c..e27455d6381f0da4d96a4241eb468c6dde0e390e 100644
>--- a/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp
>+++ b/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBase.cpp
>@@ -38,6 +38,7 @@
> #include "NativeWebMouseEvent.h"
> #include "NativeWebWheelEvent.h"
> #include "PageClientImpl.h"
>+#include "ViewGestureController.h"
> #include "WebEventFactory.h"
> #include "WebInspectorProxy.h"
> #include "WebKit2Initialize.h"
>@@ -202,6 +203,7 @@ struct _WebKitWebViewBasePrivate {
> #if HAVE(GTK_GESTURES)
>     std::unique_ptr<GestureController> gestureController;
> #endif
>+    std::unique_ptr<ViewGestureController> viewGestureController;
> };
> 
> WEBKIT_DEFINE_TYPE(WebKitWebViewBase, webkit_web_view_base, GTK_TYPE_CONTAINER)
>@@ -536,6 +538,10 @@ static gboolean webkitWebViewBaseDraw(GtkWidget* widget, cairo_t* cr)
>     if (!gdk_cairo_get_clip_rectangle(cr, &clipRect))
>         return FALSE;
> 
>+    bool showingNavigationSnapshot = webViewBase->priv->pageProxy->isShowingNavigationGestureSnapshot();
>+    if (showingNavigationSnapshot)
>+        cairo_push_group(cr);
>+
>     if (webViewBase->priv->acceleratedBackingStore && drawingArea->isInAcceleratedCompositingMode())
>         webViewBase->priv->acceleratedBackingStore->paint(cr, clipRect);
>     else {
>@@ -543,6 +549,12 @@ static gboolean webkitWebViewBaseDraw(GtkWidget* widget, cairo_t* cr)
>         drawingArea->paint(cr, clipRect, unpaintedRegion);
>     }
> 
>+    if (showingNavigationSnapshot) {
>+        ViewGestureController& controller = webkitWebViewBaseViewGestureController(webViewBase);
>+        RefPtr<cairo_pattern_t> group = adoptRef(cairo_pop_group(cr));
>+        controller.draw(cr, group.get());
>+    }
>+
>     GTK_WIDGET_CLASS(webkit_web_view_base_parent_class)->draw(widget, cr);
> 
>     return FALSE;
>@@ -855,6 +867,10 @@ static gboolean webkitWebViewBaseScrollEvent(GtkWidget* widget, GdkEventScroll*
>         }
>     }
> 
>+    ViewGestureController& controller = webkitWebViewBaseViewGestureController(webViewBase);
>+    if (controller.isSwipeGestureEnabled() && controller.handleScrollWheelEvent(event))
>+        return GDK_EVENT_STOP;
>+
>     webkitWebViewBaseHandleWheelEvent(webViewBase, reinterpret_cast<GdkEvent*>(event));
> 
>     return GDK_EVENT_STOP;
>@@ -1027,11 +1043,11 @@ static gboolean webkitWebViewBaseTouchEvent(GtkWidget* widget, GdkEventTouch* ev
> #endif // ENABLE(TOUCH_EVENTS)
> 
> #if HAVE(GTK_GESTURES)
>-class ViewGestureController final : public GestureControllerClient {
>+class TouchGestureController final : public GestureControllerClient {
>     WTF_MAKE_FAST_ALLOCATED;
> 
> public:
>-    explicit ViewGestureController(WebKitWebViewBase* webViewBase)
>+    explicit TouchGestureController(WebKitWebViewBase* webViewBase)
>         : m_webView(webViewBase)
>     {
>     }
>@@ -1146,11 +1162,16 @@ GestureController& webkitWebViewBaseGestureController(WebKitWebViewBase* webView
> {
>     WebKitWebViewBasePrivate* priv = webViewBase->priv;
>     if (!priv->gestureController)
>-        priv->gestureController = std::make_unique<GestureController>(GTK_WIDGET(webViewBase), std::make_unique<ViewGestureController>(webViewBase));
>+        priv->gestureController = std::make_unique<GestureController>(GTK_WIDGET(webViewBase), std::make_unique<TouchGestureController>(webViewBase));
>     return *priv->gestureController;
> }
> #endif
> 
>+ViewGestureController& webkitWebViewBaseViewGestureController(WebKitWebViewBase* webViewBase)
>+{
>+    return *webViewBase->priv->viewGestureController;
>+}
>+
> static gboolean webkitWebViewBaseQueryTooltip(GtkWidget* widget, gint /* x */, gint /* y */, gboolean keyboardMode, GtkTooltip* tooltip)
> {
>     WebKitWebViewBasePrivate* priv = WEBKIT_WEB_VIEW_BASE(widget)->priv;
>@@ -1388,6 +1409,8 @@ void webkitWebViewBaseCreateWebPage(WebKitWebViewBase* webkitWebViewBase, Ref<AP
>     priv->pageProxy->setIntrinsicDeviceScaleFactor(gtk_widget_get_scale_factor(GTK_WIDGET(webkitWebViewBase)));
>     g_signal_connect(webkitWebViewBase, "notify::scale-factor", G_CALLBACK(deviceScaleFactorChanged), nullptr);
> #endif
>+
>+    priv->viewGestureController = std::make_unique<WebKit::ViewGestureController>(*priv->pageProxy);
> }
> 
> void webkitWebViewBaseSetTooltipText(WebKitWebViewBase* webViewBase, const char* tooltip)
>@@ -1640,3 +1663,62 @@ void webkitWebViewBasePageClosed(WebKitWebViewBase* webkitWebViewBase)
>     drawingArea->destroyNativeSurfaceHandleForCompositing();
> #endif
> }
>+
>+RefPtr<WebKit::ViewSnapshot> webkitWebViewBaseTakeViewSnapshot(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    WebPageProxy* page = webkitWebViewBase->priv->pageProxy.get();
>+
>+    IntSize size = page->viewSize();
>+
>+#if HAVE_GTK_SCALE_FACTOR
>+    float deviceScale = page->deviceScaleFactor();
>+    size.scale(deviceScale);
>+#endif
>+
>+    RefPtr<cairo_surface_t> surface = adoptRef(cairo_image_surface_create(CAIRO_FORMAT_RGB24, size.width(), size.height()));
>+
>+#if HAVE_GTK_SCALE_FACTOR
>+    cairoSurfaceSetDeviceScale(surface.get(), deviceScale, deviceScale);
>+#endif
>+
>+    RefPtr<cairo_t> cr = adoptRef(cairo_create(surface.get()));
>+    webkitWebViewBaseDraw(GTK_WIDGET(webkitWebViewBase), cr.get());
>+
>+    return ViewSnapshot::create(WTFMove(surface));
>+}
>+
>+void webkitWebViewBaseDidStartProvisionalLoadForMainFrame(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didStartProvisionalLoadForMainFrame();
>+}
>+
>+void webkitWebViewBaseDidFirstVisuallyNonEmptyLayoutForMainFrame(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didFirstVisuallyNonEmptyLayoutForMainFrame();
>+}
>+
>+void webkitWebViewBaseDidFinishLoadForMainFrame(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didFinishLoadForMainFrame();
>+}
>+
>+void webkitWebViewBaseDidFailLoadForMainFrame(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didFailLoadForMainFrame();
>+}
>+
>+void webkitWebViewBaseDidSameDocumentNavigationForMainFrame(WebKitWebViewBase* webkitWebViewBase, SameDocumentNavigationType type)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didSameDocumentNavigationForMainFrame(type);
>+}
>+
>+void webkitWebViewBaseDidRestoreScrollPosition(WebKitWebViewBase* webkitWebViewBase)
>+{
>+    if (webkitWebViewBase->priv->viewGestureController->isSwipeGestureEnabled())
>+        webkitWebViewBase->priv->viewGestureController->didRestoreScrollPosition();
>+}
>diff --git a/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h b/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h
>index 8dde69b1bb8cb59bcdd05ea66f77eef0cf9700ea..1360285bfa236b4c35c7444f259e1698f4a0451f 100644
>--- a/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h
>+++ b/Source/WebKit/UIProcess/API/gtk/WebKitWebViewBasePrivate.h
>@@ -30,6 +30,9 @@
> #include "APIPageConfiguration.h"
> #include "DragAndDropHandler.h"
> #include "GestureController.h"
>+#include "SameDocumentNavigationType.h"
>+#include "ViewGestureController.h"
>+#include "ViewSnapshotStore.h"
> #include "WebContextMenuProxyGtk.h"
> #include "WebInspectorProxy.h"
> #include "WebKitWebViewBase.h"
>@@ -78,3 +81,14 @@ WebKit::DragAndDropHandler& webkitWebViewBaseDragAndDropHandler(WebKitWebViewBas
> #if HAVE(GTK_GESTURES)
> WebKit::GestureController& webkitWebViewBaseGestureController(WebKitWebViewBase*);
> #endif
>+
>+RefPtr<WebKit::ViewSnapshot> webkitWebViewBaseTakeViewSnapshot(WebKitWebViewBase*);
>+
>+WebKit::ViewGestureController& webkitWebViewBaseViewGestureController(WebKitWebViewBase*);
>+
>+void webkitWebViewBaseDidStartProvisionalLoadForMainFrame(WebKitWebViewBase*);
>+void webkitWebViewBaseDidFirstVisuallyNonEmptyLayoutForMainFrame(WebKitWebViewBase*);
>+void webkitWebViewBaseDidFinishLoadForMainFrame(WebKitWebViewBase*);
>+void webkitWebViewBaseDidFailLoadForMainFrame(WebKitWebViewBase*);
>+void webkitWebViewBaseDidSameDocumentNavigationForMainFrame(WebKitWebViewBase*, WebKit::SameDocumentNavigationType);
>+void webkitWebViewBaseDidRestoreScrollPosition(WebKitWebViewBase*);
>diff --git a/Source/WebKit/UIProcess/API/gtk/docs/webkit2gtk-4.0-sections.txt b/Source/WebKit/UIProcess/API/gtk/docs/webkit2gtk-4.0-sections.txt
>index 24d7269eb98329681cddaee9f7890f5e6c4cc1da..6088fcf7fc3b467541dcbbb90aecfa65f8207201 100644
>--- a/Source/WebKit/UIProcess/API/gtk/docs/webkit2gtk-4.0-sections.txt
>+++ b/Source/WebKit/UIProcess/API/gtk/docs/webkit2gtk-4.0-sections.txt
>@@ -488,6 +488,8 @@ webkit_settings_get_allow_universal_access_from_file_urls
> webkit_settings_set_allow_universal_access_from_file_urls
> webkit_settings_get_hardware_acceleration_policy
> webkit_settings_set_hardware_acceleration_policy
>+webkit_settings_get_enable_back_forward_navigation_gestures
>+webkit_settings_set_enable_back_forward_navigation_gestures
> webkit_settings_font_size_to_points
> webkit_settings_font_size_to_pixels
> 
>diff --git a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.cpp b/Source/WebKit/UIProcess/Cocoa/ViewGestureController.cpp
>deleted file mode 100644
>index bd041dd200ffd6e8bb487acf44471c2afd56ea97..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.cpp
>+++ /dev/null
>@@ -1,376 +0,0 @@
>-/*
>- * Copyright (C) 2013-2015 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#import "config.h"
>-#import "ViewGestureController.h"
>-
>-#import "Logging.h"
>-#import "RemoteLayerTreeDrawingAreaProxy.h"
>-#import "ViewGestureControllerMessages.h"
>-#import "WebBackForwardList.h"
>-#import "WebFullScreenManagerProxy.h"
>-#import "WebPageProxy.h"
>-#import "WebProcessProxy.h"
>-#import <wtf/MathExtras.h>
>-#import <wtf/NeverDestroyed.h>
>-#import <wtf/text/StringBuilder.h>
>-#import <wtf/text/StringConcatenateNumbers.h>
>-
>-namespace WebKit {
>-using namespace WebCore;
>-
>-static const Seconds swipeSnapshotRemovalWatchdogAfterFirstVisuallyNonEmptyLayoutDuration { 3_s };
>-static const Seconds swipeSnapshotRemovalActiveLoadMonitoringInterval { 250_ms };
>-
>-#if PLATFORM(MAC)
>-static const Seconds swipeSnapshotRemovalWatchdogDuration = 5_s;
>-#else
>-static const Seconds swipeSnapshotRemovalWatchdogDuration = 3_s;
>-#endif
>-
>-static HashMap<uint64_t, ViewGestureController*>& viewGestureControllersForAllPages()
>-{
>-    // The key in this map is the associated page ID.
>-    static NeverDestroyed<HashMap<uint64_t, ViewGestureController*>> viewGestureControllers;
>-    return viewGestureControllers.get();
>-}
>-
>-ViewGestureController::ViewGestureController(WebPageProxy& webPageProxy)
>-    : m_webPageProxy(webPageProxy)
>-    , m_swipeActiveLoadMonitoringTimer(RunLoop::main(), this, &ViewGestureController::checkForActiveLoads)
>-#if PLATFORM(MAC)
>-    , m_pendingSwipeTracker(webPageProxy, *this)
>-#endif
>-{
>-    connectToProcess();
>-
>-    viewGestureControllersForAllPages().add(webPageProxy.pageID(), this);
>-}
>-
>-ViewGestureController::~ViewGestureController()
>-{
>-    platformTeardown();
>-
>-    viewGestureControllersForAllPages().remove(m_webPageProxy.pageID());
>-
>-    disconnectFromProcess();
>-}
>-
>-void ViewGestureController::disconnectFromProcess()
>-{
>-    if (!m_isConnectedToProcess)
>-        return;
>-
>-    m_webPageProxy.process().removeMessageReceiver(Messages::ViewGestureController::messageReceiverName(), m_webPageProxy.pageID());
>-    m_isConnectedToProcess = false;
>-}
>-
>-void ViewGestureController::connectToProcess()
>-{
>-    if (m_isConnectedToProcess)
>-        return;
>-
>-    m_webPageProxy.process().addMessageReceiver(Messages::ViewGestureController::messageReceiverName(), m_webPageProxy.pageID(), *this);
>-    m_isConnectedToProcess = true;
>-}
>-
>-ViewGestureController* ViewGestureController::controllerForGesture(uint64_t pageID, ViewGestureController::GestureID gestureID)
>-{
>-    auto gestureControllerIter = viewGestureControllersForAllPages().find(pageID);
>-    if (gestureControllerIter == viewGestureControllersForAllPages().end())
>-        return nullptr;
>-    if (gestureControllerIter->value->m_currentGestureID != gestureID)
>-        return nullptr;
>-    return gestureControllerIter->value;
>-}
>-
>-ViewGestureController::GestureID ViewGestureController::takeNextGestureID()
>-{
>-    static GestureID nextGestureID;
>-    return ++nextGestureID;
>-}
>-
>-void ViewGestureController::willBeginGesture(ViewGestureType type)
>-{
>-    m_activeGestureType = type;
>-    m_currentGestureID = takeNextGestureID();
>-}
>-
>-void ViewGestureController::didEndGesture()
>-{
>-    m_activeGestureType = ViewGestureType::None;
>-    m_currentGestureID = 0;
>-}
>-    
>-void ViewGestureController::setAlternateBackForwardListSourcePage(WebPageProxy* page)
>-{
>-    m_alternateBackForwardListSourcePage = makeWeakPtr(page);
>-}
>-    
>-bool ViewGestureController::canSwipeInDirection(SwipeDirection direction) const
>-{
>-    if (!m_swipeGestureEnabled)
>-        return false;
>-
>-#if ENABLE(FULLSCREEN_API)
>-    if (m_webPageProxy.fullScreenManager() && m_webPageProxy.fullScreenManager()->isFullScreen())
>-        return false;
>-#endif
>-
>-    RefPtr<WebPageProxy> alternateBackForwardListSourcePage = m_alternateBackForwardListSourcePage.get();
>-    auto& backForwardList = alternateBackForwardListSourcePage ? alternateBackForwardListSourcePage->backForwardList() : m_webPageProxy.backForwardList();
>-    if (direction == SwipeDirection::Back)
>-        return !!backForwardList.backItem();
>-    return !!backForwardList.forwardItem();
>-}
>-
>-void ViewGestureController::didStartProvisionalOrSameDocumentLoadForMainFrame()
>-{
>-    m_snapshotRemovalTracker.resume();
>-#if PLATFORM(MAC)
>-    requestRenderTreeSizeNotificationIfNeeded();
>-#endif
>-
>-    if (auto loadCallback = WTFMove(m_loadCallback))
>-        loadCallback();
>-}
>-
>-void ViewGestureController::didStartProvisionalLoadForMainFrame()
>-{
>-    didStartProvisionalOrSameDocumentLoadForMainFrame();
>-}
>-
>-void ViewGestureController::didFirstVisuallyNonEmptyLayoutForMainFrame()
>-{
>-    if (!m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::VisuallyNonEmptyLayout))
>-        return;
>-
>-    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::MainFrameLoad);
>-    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::SubresourceLoads);
>-    m_snapshotRemovalTracker.startWatchdog(swipeSnapshotRemovalWatchdogAfterFirstVisuallyNonEmptyLayoutDuration);
>-}
>-
>-void ViewGestureController::didRepaintAfterNavigation()
>-{
>-    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::RepaintAfterNavigation);
>-}
>-
>-void ViewGestureController::didHitRenderTreeSizeThreshold()
>-{
>-    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::RenderTreeSizeThreshold);
>-}
>-
>-void ViewGestureController::didRestoreScrollPosition()
>-{
>-    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::ScrollPositionRestoration);
>-}
>-
>-void ViewGestureController::didReachMainFrameLoadTerminalState()
>-{
>-    if (m_snapshotRemovalTracker.isPaused() && m_snapshotRemovalTracker.hasRemovalCallback()) {
>-        removeSwipeSnapshot();
>-        return;
>-    }
>-
>-    if (!m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::MainFrameLoad))
>-        return;
>-
>-    // Coming back from the page cache will result in getting a load event, but no first visually non-empty layout.
>-    // WebCore considers a loaded document enough to be considered visually non-empty, so that's good
>-    // enough for us too.
>-    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::VisuallyNonEmptyLayout);
>-
>-    checkForActiveLoads();
>-}
>-
>-void ViewGestureController::didSameDocumentNavigationForMainFrame(SameDocumentNavigationType type)
>-{
>-    didStartProvisionalOrSameDocumentLoadForMainFrame();
>-
>-    bool cancelledOutstandingEvent = false;
>-
>-    // Same-document navigations don't have a main frame load or first visually non-empty layout.
>-    cancelledOutstandingEvent |= m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::MainFrameLoad);
>-    cancelledOutstandingEvent |= m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::VisuallyNonEmptyLayout);
>-
>-    if (!cancelledOutstandingEvent)
>-        return;
>-
>-    if (type != SameDocumentNavigationSessionStateReplace && type != SameDocumentNavigationSessionStatePop)
>-        return;
>-
>-    checkForActiveLoads();
>-}
>-
>-void ViewGestureController::checkForActiveLoads()
>-{
>-    if (m_webPageProxy.pageLoadState().isLoading()) {
>-        if (!m_swipeActiveLoadMonitoringTimer.isActive())
>-            m_swipeActiveLoadMonitoringTimer.startRepeating(swipeSnapshotRemovalActiveLoadMonitoringInterval);
>-        return;
>-    }
>-
>-    m_swipeActiveLoadMonitoringTimer.stop();
>-    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::SubresourceLoads);
>-}
>-
>-ViewGestureController::SnapshotRemovalTracker::SnapshotRemovalTracker()
>-    : m_watchdogTimer(RunLoop::main(), this, &SnapshotRemovalTracker::watchdogTimerFired)
>-{
>-}
>-
>-String ViewGestureController::SnapshotRemovalTracker::eventsDescription(Events event)
>-{
>-    StringBuilder description;
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::VisuallyNonEmptyLayout)
>-        description.append("VisuallyNonEmptyLayout ");
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::RenderTreeSizeThreshold)
>-        description.append("RenderTreeSizeThreshold ");
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::RepaintAfterNavigation)
>-        description.append("RepaintAfterNavigation ");
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::MainFrameLoad)
>-        description.append("MainFrameLoad ");
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::SubresourceLoads)
>-        description.append("SubresourceLoads ");
>-
>-    if (event & ViewGestureController::SnapshotRemovalTracker::ScrollPositionRestoration)
>-        description.append("ScrollPositionRestoration ");
>-    
>-    return description.toString();
>-}
>-
>-
>-void ViewGestureController::SnapshotRemovalTracker::log(const String& log) const
>-{
>-    auto sinceStart = MonotonicTime::now() - m_startTime;
>-    RELEASE_LOG(ViewGestures, "Swipe Snapshot Removal (%0.2f ms) - %{public}s", sinceStart.milliseconds(), log.utf8().data());
>-}
>-    
>-void ViewGestureController::SnapshotRemovalTracker::resume()
>-{
>-    if (isPaused() && m_outstandingEvents)
>-        log("resume");
>-    m_paused = false;
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::start(Events desiredEvents, WTF::Function<void()>&& removalCallback)
>-{
>-    m_outstandingEvents = desiredEvents;
>-    m_removalCallback = WTFMove(removalCallback);
>-    m_startTime = MonotonicTime::now();
>-
>-    log("start");
>-
>-    startWatchdog(swipeSnapshotRemovalWatchdogDuration);
>-    
>-    // Initially start out paused; we'll resume when the load is committed.
>-    // This avoids processing callbacks from earlier loads.
>-    pause();
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::reset()
>-{
>-    if (m_outstandingEvents)
>-        log("reset; had outstanding events: " + eventsDescription(m_outstandingEvents));
>-    m_outstandingEvents = 0;
>-    m_watchdogTimer.stop();
>-    m_removalCallback = nullptr;
>-}
>-
>-bool ViewGestureController::SnapshotRemovalTracker::stopWaitingForEvent(Events event, const String& logReason)
>-{
>-    ASSERT(hasOneBitSet(event));
>-
>-    if (!(m_outstandingEvents & event))
>-        return false;
>-
>-    if (isPaused()) {
>-        log("is paused; ignoring event: " + eventsDescription(event));
>-        return false;
>-    }
>-
>-    log(logReason + eventsDescription(event));
>-
>-    m_outstandingEvents &= ~event;
>-
>-    fireRemovalCallbackIfPossible();
>-    return true;
>-}
>-
>-bool ViewGestureController::SnapshotRemovalTracker::eventOccurred(Events event)
>-{
>-    return stopWaitingForEvent(event, "outstanding event occurred: ");
>-}
>-
>-bool ViewGestureController::SnapshotRemovalTracker::cancelOutstandingEvent(Events event)
>-{
>-    return stopWaitingForEvent(event, "wait for event cancelled: ");
>-}
>-
>-bool ViewGestureController::SnapshotRemovalTracker::hasOutstandingEvent(Event event)
>-{
>-    return m_outstandingEvents & event;
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackIfPossible()
>-{
>-    if (m_outstandingEvents) {
>-        log("deferring removal; had outstanding events: " + eventsDescription(m_outstandingEvents));
>-        return;
>-    }
>-
>-    fireRemovalCallbackImmediately();
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackImmediately()
>-{
>-    m_watchdogTimer.stop();
>-
>-    auto removalCallback = WTFMove(m_removalCallback);
>-    if (removalCallback) {
>-        log("removing snapshot");
>-        reset();
>-        removalCallback();
>-    }
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::watchdogTimerFired()
>-{
>-    log("watchdog timer fired");
>-    fireRemovalCallbackImmediately();
>-}
>-
>-void ViewGestureController::SnapshotRemovalTracker::startWatchdog(Seconds duration)
>-{
>-    log(makeString("(re)started watchdog timer for ", FormattedNumber::fixedWidth(duration.seconds(), 1), " seconds"));
>-    m_watchdogTimer.startOneShot(duration);
>-}
>-
>-} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.h b/Source/WebKit/UIProcess/Cocoa/ViewGestureController.h
>deleted file mode 100644
>index 82f2dd0fdbb4bb160793146cafafd08534482b07..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.h
>+++ /dev/null
>@@ -1,333 +0,0 @@
>-/*
>- * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#ifndef ViewGestureController_h
>-#define ViewGestureController_h
>-
>-#include "MessageReceiver.h"
>-#include "SameDocumentNavigationType.h"
>-#include <WebCore/Color.h>
>-#include <WebCore/FloatRect.h>
>-#include <wtf/BlockPtr.h>
>-#include <wtf/MonotonicTime.h>
>-#include <wtf/RetainPtr.h>
>-#include <wtf/RunLoop.h>
>-#include <wtf/WeakPtr.h>
>-
>-OBJC_CLASS CALayer;
>-
>-#if PLATFORM(IOS_FAMILY)
>-OBJC_CLASS UIGestureRecognizer;
>-OBJC_CLASS UIView;
>-OBJC_CLASS WKSwipeTransitionController;
>-OBJC_CLASS _UINavigationInteractiveTransitionBase;
>-OBJC_CLASS _UIViewControllerOneToOneTransitionContext;
>-OBJC_CLASS _UIViewControllerTransitionContext;
>-#else
>-OBJC_CLASS CAGradientLayer;
>-OBJC_CLASS NSEvent;
>-OBJC_CLASS NSView;
>-OBJC_CLASS WKSwipeCancellationTracker;
>-#endif
>-
>-namespace WebCore {
>-class IOSurface;
>-}
>-
>-namespace WebKit {
>-
>-class ViewSnapshot;
>-class WebBackForwardListItem;
>-class WebPageProxy;
>-class WebProcessProxy;
>-
>-class ViewGestureController : private IPC::MessageReceiver {
>-    WTF_MAKE_FAST_ALLOCATED;
>-    WTF_MAKE_NONCOPYABLE(ViewGestureController);
>-public:
>-    ViewGestureController(WebPageProxy&);
>-    ~ViewGestureController();
>-    void platformTeardown();
>-
>-    void disconnectFromProcess();
>-    void connectToProcess();
>-    
>-    enum class ViewGestureType {
>-        None,
>-#if PLATFORM(MAC)
>-        Magnification,
>-        SmartMagnification,
>-#endif
>-        Swipe
>-    };
>-
>-    enum class SwipeDirection {
>-        Back,
>-        Forward
>-    };
>-
>-    typedef uint64_t GestureID;
>-
>-#if PLATFORM(MAC)
>-    double magnification() const;
>-
>-    void handleMagnificationGestureEvent(NSEvent *, WebCore::FloatPoint origin);
>-
>-    bool hasActiveMagnificationGesture() const { return m_activeGestureType == ViewGestureType::Magnification; }
>-
>-    void handleSmartMagnificationGesture(WebCore::FloatPoint origin);
>-
>-    bool handleScrollWheelEvent(NSEvent *);
>-    void wheelEventWasNotHandledByWebCore(NSEvent *event) { m_pendingSwipeTracker.eventWasNotHandledByWebCore(event); }
>-    void gestureEventWasNotHandledByWebCore(NSEvent *, WebCore::FloatPoint origin);
>-
>-    void setCustomSwipeViews(Vector<RetainPtr<NSView>> views) { m_customSwipeViews = WTFMove(views); }
>-    void setCustomSwipeViewsTopContentInset(float topContentInset) { m_customSwipeViewsTopContentInset = topContentInset; }
>-    WebCore::FloatRect windowRelativeBoundsForCustomSwipeViews() const;
>-    void setDidMoveSwipeSnapshotCallback(BlockPtr<void (CGRect)>&& callback) { m_didMoveSwipeSnapshotCallback = WTFMove(callback); }
>-
>-    bool shouldIgnorePinnedState() { return m_pendingSwipeTracker.shouldIgnorePinnedState(); }
>-    void setShouldIgnorePinnedState(bool ignore) { m_pendingSwipeTracker.setShouldIgnorePinnedState(ignore); }
>-
>-    bool isPhysicallySwipingLeft(SwipeDirection) const;
>-#else
>-    bool isNavigationSwipeGestureRecognizer(UIGestureRecognizer *) const;
>-    void installSwipeHandler(UIView *gestureRecognizerView, UIView *swipingView);
>-    void beginSwipeGesture(_UINavigationInteractiveTransitionBase *, SwipeDirection);
>-    void endSwipeGesture(WebBackForwardListItem* targetItem, _UIViewControllerTransitionContext *, bool cancelled);
>-    void willCommitPostSwipeTransitionLayerTree(bool);
>-    void setRenderTreeSize(uint64_t);
>-#endif
>-    
>-    void setAlternateBackForwardListSourcePage(WebPageProxy*);
>-    
>-    bool canSwipeInDirection(SwipeDirection) const;
>-
>-    WebCore::Color backgroundColorForCurrentSnapshot() const { return m_backgroundColorForCurrentSnapshot; }
>-
>-    void didStartProvisionalLoadForMainFrame();
>-    void didFinishLoadForMainFrame() { didReachMainFrameLoadTerminalState(); }
>-    void didFailLoadForMainFrame() { didReachMainFrameLoadTerminalState(); }
>-    void didFirstVisuallyNonEmptyLayoutForMainFrame();
>-    void didRepaintAfterNavigation();
>-    void didHitRenderTreeSizeThreshold();
>-    void didRestoreScrollPosition();
>-    void didReachMainFrameLoadTerminalState();
>-    void didSameDocumentNavigationForMainFrame(SameDocumentNavigationType);
>-
>-    void checkForActiveLoads();
>-
>-    void removeSwipeSnapshot();
>-
>-    void setSwipeGestureEnabled(bool enabled) { m_swipeGestureEnabled = enabled; }
>-    bool isSwipeGestureEnabled() { return m_swipeGestureEnabled; }
>-
>-    // Testing
>-    bool beginSimulatedSwipeInDirectionForTesting(SwipeDirection);
>-    bool completeSimulatedSwipeInDirectionForTesting(SwipeDirection);
>-
>-private:
>-    // IPC::MessageReceiver.
>-    void didReceiveMessage(IPC::Connection&, IPC::Decoder&) override;
>-
>-    static ViewGestureController* controllerForGesture(uint64_t pageID, GestureID);
>-
>-    static GestureID takeNextGestureID();
>-    void willBeginGesture(ViewGestureType);
>-    void didEndGesture();
>-
>-    void didStartProvisionalOrSameDocumentLoadForMainFrame();
>-
>-    class SnapshotRemovalTracker {
>-    public:
>-        enum Event : uint8_t {
>-            VisuallyNonEmptyLayout = 1 << 0,
>-            RenderTreeSizeThreshold = 1 << 1,
>-            RepaintAfterNavigation = 1 << 2,
>-            MainFrameLoad = 1 << 3,
>-            SubresourceLoads = 1 << 4,
>-            ScrollPositionRestoration = 1 << 5
>-        };
>-        typedef uint8_t Events;
>-
>-        SnapshotRemovalTracker();
>-
>-        void start(Events, WTF::Function<void()>&&);
>-        void reset();
>-        
>-        void pause() { m_paused = true; }
>-        void resume();
>-        bool isPaused() const { return m_paused; }
>-        bool hasRemovalCallback() const { return !!m_removalCallback; }
>-
>-        bool eventOccurred(Events);
>-        bool cancelOutstandingEvent(Events);
>-        bool hasOutstandingEvent(Event);
>-
>-        void startWatchdog(Seconds);
>-
>-        uint64_t renderTreeSizeThreshold() const { return m_renderTreeSizeThreshold; }
>-        void setRenderTreeSizeThreshold(uint64_t threshold) { m_renderTreeSizeThreshold = threshold; }
>-
>-    private:
>-        static String eventsDescription(Events);
>-        void log(const String&) const;
>-
>-        void fireRemovalCallbackImmediately();
>-        void fireRemovalCallbackIfPossible();
>-        void watchdogTimerFired();
>-
>-        bool stopWaitingForEvent(Events, const String& logReason);
>-
>-        Events m_outstandingEvents { 0 };
>-        WTF::Function<void()> m_removalCallback;
>-        MonotonicTime m_startTime;
>-
>-        uint64_t m_renderTreeSizeThreshold { 0 };
>-
>-        RunLoop::Timer<SnapshotRemovalTracker> m_watchdogTimer;
>-        
>-        bool m_paused { true };
>-    };
>-
>-#if PLATFORM(MAC)
>-    // Message handlers.
>-    void didCollectGeometryForMagnificationGesture(WebCore::FloatRect visibleContentBounds, bool frameHandlesMagnificationGesture);
>-    void didCollectGeometryForSmartMagnificationGesture(WebCore::FloatPoint origin, WebCore::FloatRect renderRect, WebCore::FloatRect visibleContentBounds, bool fitEntireRect, double viewportMinimumScale, double viewportMaximumScale);
>-
>-    void endMagnificationGesture();
>-
>-    WebCore::FloatPoint scaledMagnificationOrigin(WebCore::FloatPoint origin, double scale);
>-
>-    void trackSwipeGesture(NSEvent *, SwipeDirection);
>-    void beginSwipeGesture(WebBackForwardListItem* targetItem, SwipeDirection);
>-    void handleSwipeGesture(WebBackForwardListItem* targetItem, double progress, SwipeDirection);
>-    void willEndSwipeGesture(WebBackForwardListItem& targetItem, bool cancelled);
>-    void endSwipeGesture(WebBackForwardListItem* targetItem, bool cancelled);
>-    bool shouldUseSnapshotForSize(ViewSnapshot&, WebCore::FloatSize swipeLayerSize, float topContentInset);
>-
>-    CALayer *determineSnapshotLayerParent() const;
>-    CALayer *determineLayerAdjacentToSnapshotForParent(SwipeDirection, CALayer *snapshotLayerParent) const;
>-    void applyDebuggingPropertiesToSwipeViews();
>-    void didMoveSwipeSnapshotLayer();
>-
>-    void forceRepaintIfNeeded();
>-
>-    void requestRenderTreeSizeNotificationIfNeeded();
>-
>-    class PendingSwipeTracker {
>-    public:
>-        PendingSwipeTracker(WebPageProxy&, ViewGestureController&);
>-        bool handleEvent(NSEvent *);
>-        void eventWasNotHandledByWebCore(NSEvent *);
>-
>-        void reset(const char* resetReasonForLogging);
>-
>-        bool shouldIgnorePinnedState() { return m_shouldIgnorePinnedState; }
>-        void setShouldIgnorePinnedState(bool ignore) { m_shouldIgnorePinnedState = ignore; }
>-
>-    private:
>-        bool tryToStartSwipe(NSEvent *);
>-        bool scrollEventCanBecomeSwipe(NSEvent *, SwipeDirection&);
>-
>-        enum class State {
>-            None,
>-            WaitingForWebCore,
>-            InsufficientMagnitude
>-        };
>-
>-        State m_state { State::None };
>-        SwipeDirection m_direction;
>-        WebCore::FloatSize m_cumulativeDelta;
>-
>-        bool m_shouldIgnorePinnedState { false };
>-
>-        ViewGestureController& m_viewGestureController;
>-        WebPageProxy& m_webPageProxy;
>-    };
>-#endif
>-
>-    WebPageProxy& m_webPageProxy;
>-    ViewGestureType m_activeGestureType { ViewGestureType::None };
>-
>-    bool m_swipeGestureEnabled { true };
>-
>-    RunLoop::Timer<ViewGestureController> m_swipeActiveLoadMonitoringTimer;
>-
>-    WebCore::Color m_backgroundColorForCurrentSnapshot;
>-    
>-    WeakPtr<WebPageProxy> m_alternateBackForwardListSourcePage;
>-    RefPtr<WebPageProxy> m_webPageProxyForBackForwardListForCurrentSwipe;
>-
>-    GestureID m_currentGestureID;
>-
>-#if PLATFORM(MAC)
>-    RefPtr<ViewSnapshot> m_currentSwipeSnapshot;
>-
>-    double m_magnification;
>-    WebCore::FloatPoint m_magnificationOrigin;
>-
>-    WebCore::FloatRect m_lastSmartMagnificationUnscaledTargetRect;
>-    bool m_lastMagnificationGestureWasSmartMagnification { false };
>-    WebCore::FloatPoint m_lastSmartMagnificationOrigin;
>-
>-    WebCore::FloatRect m_visibleContentRect;
>-    bool m_visibleContentRectIsValid { false };
>-    bool m_frameHandlesMagnificationGesture { false };
>-
>-    RetainPtr<WKSwipeCancellationTracker> m_swipeCancellationTracker;
>-    RetainPtr<CALayer> m_swipeLayer;
>-    RetainPtr<CALayer> m_swipeSnapshotLayer;
>-    RetainPtr<CAGradientLayer> m_swipeShadowLayer;
>-    RetainPtr<CALayer> m_swipeDimmingLayer;
>-    Vector<RetainPtr<CALayer>> m_currentSwipeLiveLayers;
>-
>-    Vector<RetainPtr<NSView>> m_customSwipeViews;
>-    float m_customSwipeViewsTopContentInset { 0 };
>-    WebCore::FloatRect m_currentSwipeCustomViewBounds;
>-
>-    PendingSwipeTracker m_pendingSwipeTracker;
>-
>-    BlockPtr<void (CGRect)> m_didMoveSwipeSnapshotCallback;
>-
>-    bool m_hasOutstandingRepaintRequest { false };
>-#else    
>-    UIView *m_liveSwipeView { nullptr };
>-    RetainPtr<UIView> m_liveSwipeViewClippingView;
>-    RetainPtr<UIView> m_snapshotView;
>-    RetainPtr<UIView> m_transitionContainerView;
>-    RetainPtr<WKSwipeTransitionController> m_swipeInteractiveTransitionDelegate;
>-    RetainPtr<_UIViewControllerOneToOneTransitionContext> m_swipeTransitionContext;
>-    uint64_t m_snapshotRemovalTargetRenderTreeSize { 0 };
>-#endif
>-    bool m_isConnectedToProcess { false };
>-
>-    SnapshotRemovalTracker m_snapshotRemovalTracker;
>-    WTF::Function<void()> m_loadCallback;
>-};
>-
>-} // namespace WebKit
>-
>-#endif // ViewGestureController_h
>diff --git a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.messages.in b/Source/WebKit/UIProcess/Cocoa/ViewGestureController.messages.in
>deleted file mode 100644
>index bb1baf361949403416c8819ec275458c23c2fc9c..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/Cocoa/ViewGestureController.messages.in
>+++ /dev/null
>@@ -1,29 +0,0 @@
>-# Copyright (C) 2013 Apple Inc. All rights reserved.
>-#
>-# Redistribution and use in source and binary forms, with or without
>-# modification, are permitted provided that the following conditions
>-# are met:
>-# 1.  Redistributions of source code must retain the above copyright
>-#     notice, this list of conditions and the following disclaimer.
>-# 2.  Redistributions in binary form must reproduce the above copyright
>-#     notice, this list of conditions and the following disclaimer in the
>-#     documentation and/or other materials provided with the distribution.
>-#
>-# THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND
>-# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
>-# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
>-# DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR
>-# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
>-# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
>-# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
>-# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
>-# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>-# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>-
>-messages -> ViewGestureController {
>-#if PLATFORM(MAC)
>-    DidCollectGeometryForMagnificationGesture(WebCore::FloatRect visibleContentBounds, bool frameHandlesMagnificationGesture)
>-    DidCollectGeometryForSmartMagnificationGesture(WebCore::FloatPoint origin, WebCore::FloatRect renderRect, WebCore::FloatRect visibleContentBounds, bool fitEntireRect, double viewportMinimumScale, double viewportMaximumScale)
>-    DidHitRenderTreeSizeThreshold()
>-#endif
>-}
>diff --git a/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.h b/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.h
>deleted file mode 100644
>index 6855b0a8eb954871737af5ce4d978974607e9b8e..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.h
>+++ /dev/null
>@@ -1,32 +0,0 @@
>-/*
>- * Copyright (C) 2014 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#pragma once
>-
>-namespace WebKit {
>-
>-void installMemoryPressureHandler();
>-
>-}
>diff --git a/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm b/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm
>deleted file mode 100644
>index d4c8137def9b85f1a348683009150abe7935d1e5..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/Cocoa/WebMemoryPressureHandlerCocoa.mm
>+++ /dev/null
>@@ -1,54 +0,0 @@
>-/*
>- * Copyright (C) 2014 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#import "config.h"
>-#import "WebMemoryPressureHandlerCocoa.h"
>-
>-#import "ViewSnapshotStore.h"
>-#import "WebProcessPool.h"
>-#import <wtf/MemoryPressureHandler.h>
>-
>-namespace WebKit {
>-
>-void installMemoryPressureHandler()
>-{
>-    // FIXME: This should be able to share code with WebCore's MemoryPressureHandler (and be platform independent).
>-    // Right now it cannot because WebKit1 and WebKit2 need to be able to coexist in the UI process,
>-    // and you can only have one WebCore::MemoryPressureHandler.
>-
>-    if ([[NSUserDefaults standardUserDefaults] boolForKey:@"WebKitSuppressMemoryPressureHandler"])
>-        return;
>-
>-    auto& memoryPressureHandler = MemoryPressureHandler::singleton();
>-    memoryPressureHandler.setLowMemoryHandler([] (Critical critical, Synchronous) {
>-        ViewSnapshotStore::singleton().discardSnapshotImages();
>-
>-        for (auto* processPool : WebProcessPool::allProcessPools())
>-            processPool->handleMemoryPressureWarning(critical);
>-    });
>-    memoryPressureHandler.install();
>-}
>-
>-} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/Cocoa/WebProcessPoolCocoa.mm b/Source/WebKit/UIProcess/Cocoa/WebProcessPoolCocoa.mm
>index 2daf75571ccb1a9d705baa057ad624a5a698a439..951c110dd6264e7280193f40b3a81131d872add0 100644
>--- a/Source/WebKit/UIProcess/Cocoa/WebProcessPoolCocoa.mm
>+++ b/Source/WebKit/UIProcess/Cocoa/WebProcessPoolCocoa.mm
>@@ -36,7 +36,7 @@
> #import "TextChecker.h"
> #import "VersionChecks.h"
> #import "WKBrowsingContextControllerInternal.h"
>-#import "WebMemoryPressureHandlerCocoa.h"
>+#import "WebMemoryPressureHandler.h"
> #import "WebPageGroup.h"
> #import "WebPreferencesKeys.h"
> #import "WebProcessCreationParameters.h"
>@@ -123,7 +123,12 @@ void WebProcessPool::platformInitialize()
>     registerUserDefaultsIfNeeded();
>     registerNotificationObservers();
> 
>-    installMemoryPressureHandler();
>+    // FIXME: This should be able to share code with WebCore's MemoryPressureHandler (and be platform independent).
>+    // Right now it cannot because WebKit1 and WebKit2 need to be able to coexist in the UI process,
>+    // and you can only have one WebCore::MemoryPressureHandler.
>+
>+    if (![[NSUserDefaults standardUserDefaults] boolForKey:@"WebKitSuppressMemoryPressureHandler"])
>+        installMemoryPressureHandler();
> 
>     setLegacyCustomProtocolManagerClient(std::make_unique<LegacyCustomProtocolManagerClient>());
> }
>diff --git a/Source/WebKit/UIProcess/PageClient.h b/Source/WebKit/UIProcess/PageClient.h
>index 38c6552bb1e8a95d02a1822387a0228300f0eb80..3961ed4512a927469d45a975b29b0a725114428f 100644
>--- a/Source/WebKit/UIProcess/PageClient.h
>+++ b/Source/WebKit/UIProcess/PageClient.h
>@@ -254,7 +254,6 @@ public:
>     virtual void assistiveTechnologyMakeFirstResponder() = 0;
>     virtual void setRemoteLayerTreeRootNode(RemoteLayerTreeNode*) = 0;
>     virtual CALayer *acceleratedCompositingRootLayer() const = 0;
>-    virtual RefPtr<ViewSnapshot> takeViewSnapshot() = 0;
> #if ENABLE(MAC_GESTURE_EVENTS)
>     virtual void gestureEventWasNotHandledByWebCore(const NativeWebGestureEvent&) = 0;
> #endif
>@@ -262,6 +261,7 @@ public:
> 
> #if PLATFORM(COCOA) || PLATFORM(GTK)
>     virtual void selectionDidChange() = 0;
>+    virtual RefPtr<ViewSnapshot> takeViewSnapshot() = 0;
> #endif
> 
> #if USE(APPKIT)
>diff --git a/Source/WebKit/UIProcess/ViewGestureController.cpp b/Source/WebKit/UIProcess/ViewGestureController.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..20c031c7301c7eb40c51276ef9a784f90ac34410
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/ViewGestureController.cpp
>@@ -0,0 +1,623 @@
>+/*
>+ * Copyright (C) 2013-2015 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "ViewGestureController.h"
>+
>+#include "APINavigation.h"
>+#include "Logging.h"
>+#include "ViewGestureControllerMessages.h"
>+#include "WebBackForwardList.h"
>+#include "WebFullScreenManagerProxy.h"
>+#include "WebPageProxy.h"
>+#include "WebProcessProxy.h"
>+#include <wtf/MathExtras.h>
>+#include <wtf/NeverDestroyed.h>
>+#include <wtf/text/StringBuilder.h>
>+#include <wtf/text/StringConcatenateNumbers.h>
>+
>+#if PLATFORM(COCOA)
>+#include "RemoteLayerTreeDrawingAreaProxy.h"
>+#endif
>+
>+#if !PLATFORM(IOS_FAMILY)
>+#include "ProvisionalPageProxy.h"
>+#include "ViewGestureGeometryCollectorMessages.h"
>+#endif
>+
>+namespace WebKit {
>+using namespace WebCore;
>+
>+static const Seconds swipeSnapshotRemovalWatchdogAfterFirstVisuallyNonEmptyLayoutDuration { 3_s };
>+static const Seconds swipeSnapshotRemovalActiveLoadMonitoringInterval { 250_ms };
>+
>+#if !PLATFORM(IOS_FAMILY)
>+static const Seconds swipeSnapshotRemovalWatchdogDuration = 5_s;
>+#else
>+static const Seconds swipeSnapshotRemovalWatchdogDuration = 3_s;
>+#endif
>+
>+#if !PLATFORM(IOS_FAMILY)
>+static const float minimumHorizontalSwipeDistance = 15;
>+static const float minimumScrollEventRatioForSwipe = 0.5;
>+
>+static const float swipeSnapshotRemovalRenderTreeSizeTargetFraction = 0.5;
>+#endif
>+
>+static HashMap<uint64_t, ViewGestureController*>& viewGestureControllersForAllPages()
>+{
>+    // The key in this map is the associated page ID.
>+    static NeverDestroyed<HashMap<uint64_t, ViewGestureController*>> viewGestureControllers;
>+    return viewGestureControllers.get();
>+}
>+
>+ViewGestureController::ViewGestureController(WebPageProxy& webPageProxy)
>+    : m_webPageProxy(webPageProxy)
>+    , m_swipeActiveLoadMonitoringTimer(RunLoop::main(), this, &ViewGestureController::checkForActiveLoads)
>+#if !PLATFORM(IOS_FAMILY)
>+    , m_pendingSwipeTracker(webPageProxy, *this)
>+#endif
>+#if PLATFORM(GTK)
>+    , m_swipeProgressTracker(webPageProxy, *this)
>+#endif
>+{
>+    connectToProcess();
>+
>+    viewGestureControllersForAllPages().add(webPageProxy.pageID(), this);
>+}
>+
>+ViewGestureController::~ViewGestureController()
>+{
>+    platformTeardown();
>+
>+    viewGestureControllersForAllPages().remove(m_webPageProxy.pageID());
>+
>+    disconnectFromProcess();
>+}
>+
>+void ViewGestureController::disconnectFromProcess()
>+{
>+    if (!m_isConnectedToProcess)
>+        return;
>+
>+    m_webPageProxy.process().removeMessageReceiver(Messages::ViewGestureController::messageReceiverName(), m_webPageProxy.pageID());
>+    m_isConnectedToProcess = false;
>+}
>+
>+void ViewGestureController::connectToProcess()
>+{
>+    if (m_isConnectedToProcess)
>+        return;
>+
>+    m_webPageProxy.process().addMessageReceiver(Messages::ViewGestureController::messageReceiverName(), m_webPageProxy.pageID(), *this);
>+    m_isConnectedToProcess = true;
>+}
>+
>+ViewGestureController* ViewGestureController::controllerForGesture(uint64_t pageID, ViewGestureController::GestureID gestureID)
>+{
>+    auto gestureControllerIter = viewGestureControllersForAllPages().find(pageID);
>+    if (gestureControllerIter == viewGestureControllersForAllPages().end())
>+        return nullptr;
>+    if (gestureControllerIter->value->m_currentGestureID != gestureID)
>+        return nullptr;
>+    return gestureControllerIter->value;
>+}
>+
>+ViewGestureController::GestureID ViewGestureController::takeNextGestureID()
>+{
>+    static GestureID nextGestureID;
>+    return ++nextGestureID;
>+}
>+
>+void ViewGestureController::willBeginGesture(ViewGestureType type)
>+{
>+    m_activeGestureType = type;
>+    m_currentGestureID = takeNextGestureID();
>+}
>+
>+void ViewGestureController::didEndGesture()
>+{
>+    m_activeGestureType = ViewGestureType::None;
>+    m_currentGestureID = 0;
>+}
>+
>+void ViewGestureController::setAlternateBackForwardListSourcePage(WebPageProxy* page)
>+{
>+    m_alternateBackForwardListSourcePage = makeWeakPtr(page);
>+}
>+
>+bool ViewGestureController::canSwipeInDirection(SwipeDirection direction) const
>+{
>+    if (!m_swipeGestureEnabled)
>+        return false;
>+
>+#if ENABLE(FULLSCREEN_API)
>+    if (m_webPageProxy.fullScreenManager() && m_webPageProxy.fullScreenManager()->isFullScreen())
>+        return false;
>+#endif
>+
>+    RefPtr<WebPageProxy> alternateBackForwardListSourcePage = m_alternateBackForwardListSourcePage.get();
>+    auto& backForwardList = alternateBackForwardListSourcePage ? alternateBackForwardListSourcePage->backForwardList() : m_webPageProxy.backForwardList();
>+    if (direction == SwipeDirection::Back)
>+        return !!backForwardList.backItem();
>+    return !!backForwardList.forwardItem();
>+}
>+
>+void ViewGestureController::didStartProvisionalOrSameDocumentLoadForMainFrame()
>+{
>+    m_snapshotRemovalTracker.resume();
>+#if !PLATFORM(IOS_FAMILY)
>+    requestRenderTreeSizeNotificationIfNeeded();
>+#endif
>+
>+    if (auto loadCallback = std::exchange(m_loadCallback, nullptr))
>+        loadCallback();
>+}
>+
>+void ViewGestureController::didStartProvisionalLoadForMainFrame()
>+{
>+    didStartProvisionalOrSameDocumentLoadForMainFrame();
>+}
>+
>+void ViewGestureController::didFirstVisuallyNonEmptyLayoutForMainFrame()
>+{
>+    if (!m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::VisuallyNonEmptyLayout))
>+        return;
>+
>+    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::MainFrameLoad);
>+    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::SubresourceLoads);
>+    m_snapshotRemovalTracker.startWatchdog(swipeSnapshotRemovalWatchdogAfterFirstVisuallyNonEmptyLayoutDuration);
>+}
>+
>+void ViewGestureController::didRepaintAfterNavigation()
>+{
>+    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::RepaintAfterNavigation);
>+}
>+
>+void ViewGestureController::didHitRenderTreeSizeThreshold()
>+{
>+    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::RenderTreeSizeThreshold);
>+}
>+
>+void ViewGestureController::didRestoreScrollPosition()
>+{
>+    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::ScrollPositionRestoration);
>+}
>+
>+void ViewGestureController::didReachMainFrameLoadTerminalState()
>+{
>+    if (m_snapshotRemovalTracker.isPaused() && m_snapshotRemovalTracker.hasRemovalCallback()) {
>+        removeSwipeSnapshot();
>+        return;
>+    }
>+
>+    if (!m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::MainFrameLoad))
>+        return;
>+
>+    // Coming back from the page cache will result in getting a load event, but no first visually non-empty layout.
>+    // WebCore considers a loaded document enough to be considered visually non-empty, so that's good
>+    // enough for us too.
>+    m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::VisuallyNonEmptyLayout);
>+
>+    checkForActiveLoads();
>+}
>+
>+void ViewGestureController::didSameDocumentNavigationForMainFrame(SameDocumentNavigationType type)
>+{
>+    didStartProvisionalOrSameDocumentLoadForMainFrame();
>+
>+    bool cancelledOutstandingEvent = false;
>+
>+    // Same-document navigations don't have a main frame load or first visually non-empty layout.
>+    cancelledOutstandingEvent |= m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::MainFrameLoad);
>+    cancelledOutstandingEvent |= m_snapshotRemovalTracker.cancelOutstandingEvent(SnapshotRemovalTracker::VisuallyNonEmptyLayout);
>+
>+    if (!cancelledOutstandingEvent)
>+        return;
>+
>+    if (type != SameDocumentNavigationSessionStateReplace && type != SameDocumentNavigationSessionStatePop)
>+        return;
>+
>+    checkForActiveLoads();
>+}
>+
>+void ViewGestureController::checkForActiveLoads()
>+{
>+    if (m_webPageProxy.pageLoadState().isLoading()) {
>+        if (!m_swipeActiveLoadMonitoringTimer.isActive())
>+            m_swipeActiveLoadMonitoringTimer.startRepeating(swipeSnapshotRemovalActiveLoadMonitoringInterval);
>+        return;
>+    }
>+
>+    m_swipeActiveLoadMonitoringTimer.stop();
>+    m_snapshotRemovalTracker.eventOccurred(SnapshotRemovalTracker::SubresourceLoads);
>+}
>+
>+ViewGestureController::SnapshotRemovalTracker::SnapshotRemovalTracker()
>+    : m_watchdogTimer(RunLoop::main(), this, &SnapshotRemovalTracker::watchdogTimerFired)
>+{
>+}
>+
>+String ViewGestureController::SnapshotRemovalTracker::eventsDescription(Events event)
>+{
>+    StringBuilder description;
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::VisuallyNonEmptyLayout)
>+        description.append("VisuallyNonEmptyLayout ");
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::RenderTreeSizeThreshold)
>+        description.append("RenderTreeSizeThreshold ");
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::RepaintAfterNavigation)
>+        description.append("RepaintAfterNavigation ");
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::MainFrameLoad)
>+        description.append("MainFrameLoad ");
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::SubresourceLoads)
>+        description.append("SubresourceLoads ");
>+
>+    if (event & ViewGestureController::SnapshotRemovalTracker::ScrollPositionRestoration)
>+        description.append("ScrollPositionRestoration ");
>+
>+    return description.toString();
>+}
>+
>+
>+void ViewGestureController::SnapshotRemovalTracker::log(const String& log) const
>+{
>+    RELEASE_LOG(ViewGestures, "Swipe Snapshot Removal (%0.2f ms) - %s", (MonotonicTime::now() - m_startTime).milliseconds(), log.utf8().data());
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::resume()
>+{
>+    if (isPaused() && m_outstandingEvents)
>+        log("resume");
>+    m_paused = false;
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::start(Events desiredEvents, WTF::Function<void()>&& removalCallback)
>+{
>+    m_outstandingEvents = desiredEvents;
>+    m_removalCallback = WTFMove(removalCallback);
>+    m_startTime = MonotonicTime::now();
>+
>+    log("start");
>+
>+    startWatchdog(swipeSnapshotRemovalWatchdogDuration);
>+
>+    // Initially start out paused; we'll resume when the load is committed.
>+    // This avoids processing callbacks from earlier loads.
>+    pause();
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::reset()
>+{
>+    if (m_outstandingEvents)
>+        log("reset; had outstanding events: " + eventsDescription(m_outstandingEvents));
>+    m_outstandingEvents = 0;
>+    m_watchdogTimer.stop();
>+    m_removalCallback = nullptr;
>+}
>+
>+bool ViewGestureController::SnapshotRemovalTracker::stopWaitingForEvent(Events event, const String& logReason)
>+{
>+    ASSERT(hasOneBitSet(event));
>+
>+    if (!(m_outstandingEvents & event))
>+        return false;
>+
>+    if (isPaused()) {
>+        log("is paused; ignoring event: " + eventsDescription(event));
>+        return false;
>+    }
>+
>+    log(logReason + eventsDescription(event));
>+
>+    m_outstandingEvents &= ~event;
>+
>+    fireRemovalCallbackIfPossible();
>+    return true;
>+}
>+
>+bool ViewGestureController::SnapshotRemovalTracker::eventOccurred(Events event)
>+{
>+    return stopWaitingForEvent(event, "outstanding event occurred: ");
>+}
>+
>+bool ViewGestureController::SnapshotRemovalTracker::cancelOutstandingEvent(Events event)
>+{
>+    return stopWaitingForEvent(event, "wait for event cancelled: ");
>+}
>+
>+bool ViewGestureController::SnapshotRemovalTracker::hasOutstandingEvent(Event event)
>+{
>+    return m_outstandingEvents & event;
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackIfPossible()
>+{
>+    if (m_outstandingEvents) {
>+        log("deferring removal; had outstanding events: " + eventsDescription(m_outstandingEvents));
>+        return;
>+    }
>+
>+    fireRemovalCallbackImmediately();
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::fireRemovalCallbackImmediately()
>+{
>+    m_watchdogTimer.stop();
>+
>+    auto removalCallback = WTFMove(m_removalCallback);
>+    if (removalCallback) {
>+        log("removing snapshot");
>+        reset();
>+        removalCallback();
>+    }
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::watchdogTimerFired()
>+{
>+    log("watchdog timer fired");
>+    fireRemovalCallbackImmediately();
>+}
>+
>+void ViewGestureController::SnapshotRemovalTracker::startWatchdog(Seconds duration)
>+{
>+    log(makeString("(re)started watchdog timer for ", FormattedNumber::fixedWidth(duration.seconds(), 1), " seconds"));
>+    m_watchdogTimer.startOneShot(duration);
>+}
>+
>+#if !PLATFORM(IOS_FAMILY)
>+static bool deltaShouldCancelSwipe(FloatSize delta)
>+{
>+    return std::abs(delta.height()) >= std::abs(delta.width()) * minimumScrollEventRatioForSwipe;
>+}
>+
>+ViewGestureController::PendingSwipeTracker::PendingSwipeTracker(WebPageProxy& webPageProxy, ViewGestureController& viewGestureController)
>+    : m_viewGestureController(viewGestureController)
>+    , m_webPageProxy(webPageProxy)
>+{
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanBecomeSwipe(PlatformScrollEvent event, ViewGestureController::SwipeDirection& potentialSwipeDirection)
>+{
>+    if (!scrollEventCanStartSwipe(event) || !scrollEventCanInfluenceSwipe(event))
>+        return false;
>+
>+    FloatSize size = scrollEventGetScrollingDeltas(event);
>+
>+    if (deltaShouldCancelSwipe(size))
>+        return false;
>+
>+    bool isPinnedToLeft = m_shouldIgnorePinnedState || m_webPageProxy.isPinnedToLeftSide();
>+    bool isPinnedToRight = m_shouldIgnorePinnedState || m_webPageProxy.isPinnedToRightSide();
>+
>+    bool tryingToSwipeBack = size.width() > 0 && isPinnedToLeft;
>+    bool tryingToSwipeForward = size.width() < 0 && isPinnedToRight;
>+    if (m_webPageProxy.userInterfaceLayoutDirection() != WebCore::UserInterfaceLayoutDirection::LTR)
>+        std::swap(tryingToSwipeBack, tryingToSwipeForward);
>+
>+    if (!tryingToSwipeBack && !tryingToSwipeForward)
>+        return false;
>+
>+    potentialSwipeDirection = tryingToSwipeBack ? SwipeDirection::Back : SwipeDirection::Forward;
>+    return m_viewGestureController.canSwipeInDirection(potentialSwipeDirection);
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::handleEvent(PlatformScrollEvent event)
>+{
>+    if (scrollEventCanEndSwipe(event)) {
>+        reset("gesture ended");
>+        return false;
>+    }
>+
>+    if (m_state == State::None) {
>+        if (!scrollEventCanBecomeSwipe(event, m_direction))
>+            return false;
>+
>+        if (!m_shouldIgnorePinnedState && m_webPageProxy.willHandleHorizontalScrollEvents()) {
>+            m_state = State::WaitingForWebCore;
>+            LOG(ViewGestures, "Swipe Start Hysteresis - waiting for WebCore to handle event");
>+        }
>+    }
>+
>+    if (m_state == State::WaitingForWebCore)
>+        return false;
>+
>+    return tryToStartSwipe(event);
>+}
>+
>+void ViewGestureController::PendingSwipeTracker::eventWasNotHandledByWebCore(PlatformScrollEvent event)
>+{
>+    if (m_state != State::WaitingForWebCore)
>+        return;
>+
>+    LOG(ViewGestures, "Swipe Start Hysteresis - WebCore didn't handle event");
>+    m_state = State::None;
>+    m_cumulativeDelta = FloatSize();
>+    tryToStartSwipe(event);
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::tryToStartSwipe(PlatformScrollEvent event)
>+{
>+    ASSERT(m_state != State::WaitingForWebCore);
>+
>+    if (m_state == State::None) {
>+        SwipeDirection direction;
>+        if (!scrollEventCanBecomeSwipe(event, direction))
>+            return false;
>+    }
>+
>+    if (!scrollEventCanInfluenceSwipe(event))
>+        return false;
>+
>+    m_cumulativeDelta += scrollEventGetScrollingDeltas(event);
>+    LOG(ViewGestures, "Swipe Start Hysteresis - consumed event, cumulative delta (%0.2f, %0.2f)", m_cumulativeDelta.width(), m_cumulativeDelta.height());
>+
>+    if (deltaShouldCancelSwipe(m_cumulativeDelta)) {
>+        reset("cumulative delta became too vertical");
>+        return false;
>+    }
>+
>+    if (std::abs(m_cumulativeDelta.width()) >= minimumHorizontalSwipeDistance)
>+        m_viewGestureController.startSwipeGesture(event, m_direction);
>+    else
>+        m_state = State::InsufficientMagnitude;
>+
>+    return true;
>+}
>+
>+void ViewGestureController::PendingSwipeTracker::reset(const char* resetReasonForLogging)
>+{
>+    if (m_state != State::None)
>+        LOG(ViewGestures, "Swipe Start Hysteresis - reset; %s", resetReasonForLogging);
>+
>+    m_state = State::None;
>+    m_cumulativeDelta = FloatSize();
>+}
>+
>+void ViewGestureController::startSwipeGesture(PlatformScrollEvent event, SwipeDirection direction)
>+{
>+    ASSERT(m_activeGestureType == ViewGestureType::None);
>+
>+    m_pendingSwipeTracker.reset("starting to track swipe");
>+
>+    m_webPageProxy.recordAutomaticNavigationSnapshot();
>+
>+    RefPtr<WebBackForwardListItem> targetItem = (direction == SwipeDirection::Back) ? m_webPageProxy.backForwardList().backItem() : m_webPageProxy.backForwardList().forwardItem();
>+    if (!targetItem)
>+        return;
>+
>+    trackSwipeGesture(event, direction, targetItem);
>+}
>+
>+bool ViewGestureController::isPhysicallySwipingLeft(SwipeDirection direction) const
>+{
>+    bool isLTR = m_webPageProxy.userInterfaceLayoutDirection() == WebCore::UserInterfaceLayoutDirection::LTR;
>+    bool isSwipingForward = direction == SwipeDirection::Forward;
>+    return isLTR != isSwipingForward;
>+}
>+
>+bool ViewGestureController::shouldUseSnapshotForSize(ViewSnapshot& snapshot, FloatSize swipeLayerSize, float topContentInset)
>+{
>+    float deviceScaleFactor = m_webPageProxy.deviceScaleFactor();
>+    if (snapshot.deviceScaleFactor() != deviceScaleFactor)
>+        return false;
>+
>+    FloatSize unobscuredSwipeLayerSizeInDeviceCoordinates = swipeLayerSize - FloatSize(0, topContentInset);
>+    unobscuredSwipeLayerSizeInDeviceCoordinates.scale(deviceScaleFactor);
>+    if (snapshot.size() != unobscuredSwipeLayerSizeInDeviceCoordinates)
>+        return false;
>+
>+    return true;
>+}
>+
>+void ViewGestureController::forceRepaintIfNeeded()
>+{
>+    if (m_activeGestureType != ViewGestureType::Swipe)
>+        return;
>+
>+    if (m_hasOutstandingRepaintRequest)
>+        return;
>+
>+    m_hasOutstandingRepaintRequest = true;
>+
>+    uint64_t pageID = m_webPageProxy.pageID();
>+    GestureID gestureID = m_currentGestureID;
>+    m_webPageProxy.forceRepaint(VoidCallback::create([pageID, gestureID] (CallbackBase::Error error) {
>+        if (auto gestureController = controllerForGesture(pageID, gestureID))
>+            gestureController->removeSwipeSnapshot();
>+    }));
>+}
>+
>+void ViewGestureController::willEndSwipeGesture(WebBackForwardListItem& targetItem, bool cancelled)
>+{
>+    m_webPageProxy.navigationGestureWillEnd(!cancelled, targetItem);
>+}
>+
>+void ViewGestureController::endSwipeGesture(WebBackForwardListItem* targetItem, bool cancelled)
>+{
>+    ASSERT(m_activeGestureType == ViewGestureType::Swipe);
>+    ASSERT(targetItem);
>+
>+#if PLATFORM(MAC)
>+    m_swipeCancellationTracker = nullptr;
>+#endif
>+
>+    if (cancelled) {
>+        removeSwipeSnapshot();
>+        m_webPageProxy.navigationGestureDidEnd(false, *targetItem);
>+        return;
>+    }
>+
>+    uint64_t renderTreeSize = 0;
>+    if (ViewSnapshot* snapshot = targetItem->snapshot())
>+        renderTreeSize = snapshot->renderTreeSize();
>+    auto renderTreeSizeThreshold = renderTreeSize * swipeSnapshotRemovalRenderTreeSizeTargetFraction;
>+
>+    m_webPageProxy.navigationGestureDidEnd(true, *targetItem);
>+    m_webPageProxy.goToBackForwardItem(*targetItem);
>+
>+    auto* currentItem = m_webPageProxy.backForwardList().currentItem();
>+    // The main frame will not be navigated so hide the snapshot right away.
>+    if (currentItem && currentItem->itemIsClone(*targetItem)) {
>+        removeSwipeSnapshot();
>+        return;
>+    }
>+
>+    SnapshotRemovalTracker::Events desiredEvents = SnapshotRemovalTracker::VisuallyNonEmptyLayout
>+        | SnapshotRemovalTracker::MainFrameLoad
>+        | SnapshotRemovalTracker::SubresourceLoads
>+        | SnapshotRemovalTracker::ScrollPositionRestoration;
>+
>+    if (renderTreeSizeThreshold) {
>+        desiredEvents |= SnapshotRemovalTracker::RenderTreeSizeThreshold;
>+        m_snapshotRemovalTracker.setRenderTreeSizeThreshold(renderTreeSizeThreshold);
>+    }
>+
>+    m_snapshotRemovalTracker.start(desiredEvents, [this] { this->forceRepaintIfNeeded(); });
>+
>+    // FIXME: Like on iOS, we should ensure that even if one of the timeouts fires,
>+    // we never show the old page content, instead showing the snapshot background color.
>+
>+    if (ViewSnapshot* snapshot = targetItem->snapshot())
>+        m_backgroundColorForCurrentSnapshot = snapshot->backgroundColor();
>+}
>+
>+void ViewGestureController::requestRenderTreeSizeNotificationIfNeeded()
>+{
>+    if (!m_snapshotRemovalTracker.hasOutstandingEvent(SnapshotRemovalTracker::RenderTreeSizeThreshold))
>+        return;
>+
>+    auto& process = m_webPageProxy.provisionalPageProxy() ? m_webPageProxy.provisionalPageProxy()->process() : m_webPageProxy.process();
>+    auto threshold = m_snapshotRemovalTracker.renderTreeSizeThreshold();
>+
>+    process.send(Messages::ViewGestureGeometryCollector::SetRenderTreeSizeNotificationThreshold(threshold), m_webPageProxy.pageID());
>+}
>+#endif
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/ViewGestureController.h b/Source/WebKit/UIProcess/ViewGestureController.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..b5411bb95af5bdf8260c53387335bb326500469c
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/ViewGestureController.h
>@@ -0,0 +1,416 @@
>+/*
>+ * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#pragma once
>+
>+#include "MessageReceiver.h"
>+#include "SameDocumentNavigationType.h"
>+#include <WebCore/Color.h>
>+#include <WebCore/FloatRect.h>
>+#include <wtf/MonotonicTime.h>
>+#include <wtf/RetainPtr.h>
>+#include <wtf/RunLoop.h>
>+#include <wtf/WeakPtr.h>
>+
>+#if PLATFORM(COCOA)
>+#include <wtf/BlockPtr.h>
>+#endif
>+
>+#if PLATFORM(GTK)
>+#include <WebCore/CairoUtilities.h>
>+#include <gtk/gtk.h>
>+#endif
>+
>+#if PLATFORM(COCOA)
>+OBJC_CLASS CALayer;
>+
>+#if PLATFORM(IOS_FAMILY)
>+OBJC_CLASS UIGestureRecognizer;
>+OBJC_CLASS UIView;
>+OBJC_CLASS WKSwipeTransitionController;
>+OBJC_CLASS _UINavigationInteractiveTransitionBase;
>+OBJC_CLASS _UIViewControllerOneToOneTransitionContext;
>+OBJC_CLASS _UIViewControllerTransitionContext;
>+#else
>+OBJC_CLASS CAGradientLayer;
>+OBJC_CLASS NSEvent;
>+OBJC_CLASS NSView;
>+OBJC_CLASS WKSwipeCancellationTracker;
>+#endif
>+
>+namespace WebCore {
>+class IOSurface;
>+}
>+#endif
>+
>+#if PLATFORM(MAC)
>+typedef NSEvent* PlatformScrollEvent;
>+#elif PLATFORM(GTK)
>+typedef struct _GdkEventScroll GdkEventScroll;
>+typedef GdkEventScroll* PlatformScrollEvent;
>+#endif
>+
>+namespace WebKit {
>+
>+class ViewSnapshot;
>+class WebBackForwardListItem;
>+class WebPageProxy;
>+class WebProcessProxy;
>+
>+class ViewGestureController : private IPC::MessageReceiver {
>+    WTF_MAKE_FAST_ALLOCATED;
>+    WTF_MAKE_NONCOPYABLE(ViewGestureController);
>+public:
>+    ViewGestureController(WebPageProxy&);
>+    ~ViewGestureController();
>+    void platformTeardown();
>+
>+    void disconnectFromProcess();
>+    void connectToProcess();
>+
>+    enum class ViewGestureType {
>+        None,
>+#if PLATFORM(MAC)
>+        Magnification,
>+        SmartMagnification,
>+#endif
>+        Swipe
>+    };
>+
>+    enum class SwipeDirection {
>+        Back,
>+        Forward
>+    };
>+
>+    typedef uint64_t GestureID;
>+
>+#if !PLATFORM(IOS_FAMILY)
>+    bool handleScrollWheelEvent(PlatformScrollEvent);
>+    void wheelEventWasNotHandledByWebCore(PlatformScrollEvent event) { m_pendingSwipeTracker.eventWasNotHandledByWebCore(event); }
>+
>+    bool shouldIgnorePinnedState() { return m_pendingSwipeTracker.shouldIgnorePinnedState(); }
>+    void setShouldIgnorePinnedState(bool ignore) { m_pendingSwipeTracker.setShouldIgnorePinnedState(ignore); }
>+
>+    bool isPhysicallySwipingLeft(SwipeDirection) const;
>+#endif
>+
>+#if PLATFORM(MAC)
>+    double magnification() const;
>+
>+    void handleMagnificationGestureEvent(PlatformScrollEvent, WebCore::FloatPoint origin);
>+
>+    bool hasActiveMagnificationGesture() const { return m_activeGestureType == ViewGestureType::Magnification; }
>+
>+    void handleSmartMagnificationGesture(WebCore::FloatPoint origin);
>+
>+    void gestureEventWasNotHandledByWebCore(PlatformScrollEvent, WebCore::FloatPoint origin);
>+
>+    void setCustomSwipeViews(Vector<RetainPtr<NSView>> views) { m_customSwipeViews = WTFMove(views); }
>+    void setCustomSwipeViewsTopContentInset(float topContentInset) { m_customSwipeViewsTopContentInset = topContentInset; }
>+    WebCore::FloatRect windowRelativeBoundsForCustomSwipeViews() const;
>+    void setDidMoveSwipeSnapshotCallback(BlockPtr<void (CGRect)>&& callback) { m_didMoveSwipeSnapshotCallback = WTFMove(callback); }
>+#elif PLATFORM(IOS_FAMILY)
>+    bool isNavigationSwipeGestureRecognizer(UIGestureRecognizer *) const;
>+    void installSwipeHandler(UIView *gestureRecognizerView, UIView *swipingView);
>+    void beginSwipeGesture(_UINavigationInteractiveTransitionBase *, SwipeDirection);
>+    void endSwipeGesture(WebBackForwardListItem* targetItem, _UIViewControllerTransitionContext *, bool cancelled);
>+    void willCommitPostSwipeTransitionLayerTree(bool);
>+    void setRenderTreeSize(uint64_t);
>+#endif
>+
>+    void setAlternateBackForwardListSourcePage(WebPageProxy*);
>+
>+    bool canSwipeInDirection(SwipeDirection) const;
>+
>+    WebCore::Color backgroundColorForCurrentSnapshot() const { return m_backgroundColorForCurrentSnapshot; }
>+
>+    void didStartProvisionalLoadForMainFrame();
>+    void didFinishLoadForMainFrame() { didReachMainFrameLoadTerminalState(); }
>+    void didFailLoadForMainFrame() { didReachMainFrameLoadTerminalState(); }
>+    void didFirstVisuallyNonEmptyLayoutForMainFrame();
>+    void didRepaintAfterNavigation();
>+    void didHitRenderTreeSizeThreshold();
>+    void didRestoreScrollPosition();
>+    void didReachMainFrameLoadTerminalState();
>+    void didSameDocumentNavigationForMainFrame(SameDocumentNavigationType);
>+
>+    void checkForActiveLoads();
>+
>+    void removeSwipeSnapshot();
>+
>+    void setSwipeGestureEnabled(bool enabled) { m_swipeGestureEnabled = enabled; }
>+    bool isSwipeGestureEnabled() { return m_swipeGestureEnabled; }
>+
>+#if PLATFORM(GTK)
>+    void draw(cairo_t*, cairo_pattern_t*);
>+#endif
>+
>+    // Testing
>+    bool beginSimulatedSwipeInDirectionForTesting(SwipeDirection);
>+    bool completeSimulatedSwipeInDirectionForTesting(SwipeDirection);
>+
>+private:
>+    // IPC::MessageReceiver.
>+    void didReceiveMessage(IPC::Connection&, IPC::Decoder&) override;
>+
>+    static ViewGestureController* controllerForGesture(uint64_t pageID, GestureID);
>+
>+    static GestureID takeNextGestureID();
>+    void willBeginGesture(ViewGestureType);
>+    void didEndGesture();
>+
>+    void didStartProvisionalOrSameDocumentLoadForMainFrame();
>+
>+    class SnapshotRemovalTracker {
>+    public:
>+        enum Event : uint8_t {
>+            VisuallyNonEmptyLayout = 1 << 0,
>+            RenderTreeSizeThreshold = 1 << 1,
>+            RepaintAfterNavigation = 1 << 2,
>+            MainFrameLoad = 1 << 3,
>+            SubresourceLoads = 1 << 4,
>+            ScrollPositionRestoration = 1 << 5
>+        };
>+        typedef uint8_t Events;
>+
>+        SnapshotRemovalTracker();
>+
>+        void start(Events, WTF::Function<void()>&&);
>+        void reset();
>+
>+        void pause() { m_paused = true; }
>+        void resume();
>+        bool isPaused() const { return m_paused; }
>+        bool hasRemovalCallback() const { return !!m_removalCallback; }
>+
>+        bool eventOccurred(Events);
>+        bool cancelOutstandingEvent(Events);
>+        bool hasOutstandingEvent(Event);
>+
>+        void startWatchdog(Seconds);
>+
>+        uint64_t renderTreeSizeThreshold() const { return m_renderTreeSizeThreshold; }
>+        void setRenderTreeSizeThreshold(uint64_t threshold) { m_renderTreeSizeThreshold = threshold; }
>+
>+    private:
>+        static String eventsDescription(Events);
>+        void log(const String&) const;
>+
>+        void fireRemovalCallbackImmediately();
>+        void fireRemovalCallbackIfPossible();
>+        void watchdogTimerFired();
>+
>+        bool stopWaitingForEvent(Events, const String& logReason);
>+
>+        Events m_outstandingEvents { 0 };
>+        WTF::Function<void()> m_removalCallback;
>+        MonotonicTime m_startTime;
>+
>+        uint64_t m_renderTreeSizeThreshold { 0 };
>+
>+        RunLoop::Timer<SnapshotRemovalTracker> m_watchdogTimer;
>+
>+        bool m_paused { true };
>+    };
>+
>+#if PLATFORM(MAC)
>+    // Message handlers.
>+    void didCollectGeometryForMagnificationGesture(WebCore::FloatRect visibleContentBounds, bool frameHandlesMagnificationGesture);
>+    void didCollectGeometryForSmartMagnificationGesture(WebCore::FloatPoint origin, WebCore::FloatRect renderRect, WebCore::FloatRect visibleContentBounds, bool fitEntireRect, double viewportMinimumScale, double viewportMaximumScale);
>+
>+    void endMagnificationGesture();
>+
>+    WebCore::FloatPoint scaledMagnificationOrigin(WebCore::FloatPoint origin, double scale);
>+#endif
>+
>+#if !PLATFORM(IOS_FAMILY)
>+    void startSwipeGesture(PlatformScrollEvent, SwipeDirection);
>+    void trackSwipeGesture(PlatformScrollEvent, SwipeDirection, RefPtr<WebBackForwardListItem>);
>+
>+    void beginSwipeGesture(WebBackForwardListItem* targetItem, SwipeDirection);
>+    void handleSwipeGesture(WebBackForwardListItem* targetItem, double progress, SwipeDirection);
>+
>+    void willEndSwipeGesture(WebBackForwardListItem& targetItem, bool cancelled);
>+    void endSwipeGesture(WebBackForwardListItem* targetItem, bool cancelled);
>+    bool shouldUseSnapshotForSize(ViewSnapshot&, WebCore::FloatSize swipeLayerSize, float topContentInset);
>+
>+#if PLATFORM(MAC)
>+    CALayer* determineSnapshotLayerParent() const;
>+    CALayer* determineLayerAdjacentToSnapshotForParent(SwipeDirection, CALayer* snapshotLayerParent) const;
>+    void applyDebuggingPropertiesToSwipeViews();
>+    void didMoveSwipeSnapshotLayer();
>+#endif
>+
>+    void requestRenderTreeSizeNotificationIfNeeded();
>+    void forceRepaintIfNeeded();
>+
>+    class PendingSwipeTracker {
>+    public:
>+        PendingSwipeTracker(WebPageProxy&, ViewGestureController&);
>+        bool handleEvent(PlatformScrollEvent);
>+        void eventWasNotHandledByWebCore(PlatformScrollEvent);
>+
>+        void reset(const char* resetReasonForLogging);
>+
>+        bool shouldIgnorePinnedState() { return m_shouldIgnorePinnedState; }
>+        void setShouldIgnorePinnedState(bool ignore) { m_shouldIgnorePinnedState = ignore; }
>+
>+    private:
>+        bool tryToStartSwipe(PlatformScrollEvent);
>+        bool scrollEventCanBecomeSwipe(PlatformScrollEvent, SwipeDirection&);
>+
>+        bool scrollEventCanStartSwipe(PlatformScrollEvent);
>+        bool scrollEventCanEndSwipe(PlatformScrollEvent);
>+        bool scrollEventCanInfluenceSwipe(PlatformScrollEvent);
>+        WebCore::FloatSize scrollEventGetScrollingDeltas(PlatformScrollEvent);
>+
>+        enum class State {
>+            None,
>+            WaitingForWebCore,
>+            InsufficientMagnitude
>+        };
>+
>+        State m_state { State::None };
>+        SwipeDirection m_direction;
>+        WebCore::FloatSize m_cumulativeDelta;
>+
>+        bool m_shouldIgnorePinnedState { false };
>+
>+        ViewGestureController& m_viewGestureController;
>+        WebPageProxy& m_webPageProxy;
>+    };
>+#endif
>+
>+    WebPageProxy& m_webPageProxy;
>+    ViewGestureType m_activeGestureType { ViewGestureType::None };
>+
>+    bool m_swipeGestureEnabled { true };
>+
>+    RunLoop::Timer<ViewGestureController> m_swipeActiveLoadMonitoringTimer;
>+
>+    WebCore::Color m_backgroundColorForCurrentSnapshot;
>+
>+    WeakPtr<WebPageProxy> m_alternateBackForwardListSourcePage;
>+    RefPtr<WebPageProxy> m_webPageProxyForBackForwardListForCurrentSwipe;
>+
>+    GestureID m_currentGestureID;
>+
>+#if !PLATFORM(IOS_FAMILY)
>+    RefPtr<ViewSnapshot> m_currentSwipeSnapshot;
>+
>+    PendingSwipeTracker m_pendingSwipeTracker;
>+
>+    bool m_hasOutstandingRepaintRequest { false };
>+#endif
>+
>+#if PLATFORM(MAC)
>+    double m_magnification;
>+    WebCore::FloatPoint m_magnificationOrigin;
>+
>+    WebCore::FloatRect m_lastSmartMagnificationUnscaledTargetRect;
>+    bool m_lastMagnificationGestureWasSmartMagnification { false };
>+    WebCore::FloatPoint m_lastSmartMagnificationOrigin;
>+
>+    WebCore::FloatRect m_visibleContentRect;
>+    bool m_visibleContentRectIsValid { false };
>+    bool m_frameHandlesMagnificationGesture { false };
>+
>+    RetainPtr<WKSwipeCancellationTracker> m_swipeCancellationTracker;
>+    RetainPtr<CALayer> m_swipeLayer;
>+    RetainPtr<CALayer> m_swipeSnapshotLayer;
>+    RetainPtr<CAGradientLayer> m_swipeShadowLayer;
>+    RetainPtr<CALayer> m_swipeDimmingLayer;
>+    Vector<RetainPtr<CALayer>> m_currentSwipeLiveLayers;
>+
>+    Vector<RetainPtr<NSView>> m_customSwipeViews;
>+    float m_customSwipeViewsTopContentInset { 0 };
>+    WebCore::FloatRect m_currentSwipeCustomViewBounds;
>+
>+    BlockPtr<void (CGRect)> m_didMoveSwipeSnapshotCallback;
>+#elif PLATFORM(IOS_FAMILY)
>+    UIView* m_liveSwipeView { nullptr };
>+    RetainPtr<UIView> m_liveSwipeViewClippingView;
>+    RetainPtr<UIView> m_snapshotView;
>+    RetainPtr<UIView> m_transitionContainerView;
>+    RetainPtr<WKSwipeTransitionController> m_swipeInteractiveTransitionDelegate;
>+    RetainPtr<_UIViewControllerOneToOneTransitionContext> m_swipeTransitionContext;
>+    uint64_t m_snapshotRemovalTargetRenderTreeSize { 0 };
>+#endif
>+
>+#if PLATFORM(GTK)
>+    class SwipeProgressTracker {
>+    public:
>+        SwipeProgressTracker(WebPageProxy&, ViewGestureController&);
>+        void startTracking(RefPtr<WebBackForwardListItem>&&, SwipeDirection);
>+        void reset();
>+        bool handleEvent(PlatformScrollEvent);
>+        float progress() const { return m_progress; }
>+        SwipeDirection direction() const { return m_direction; }
>+
>+    private:
>+        enum class State {
>+            None,
>+            Pending,
>+            Scrolling,
>+            Animating
>+        };
>+
>+        void startAnimation();
>+        gboolean onAnimationTick(GdkFrameClock*);
>+        void endAnimation();
>+
>+        State m_state { State::None };
>+
>+        SwipeDirection m_direction;
>+        RefPtr<WebBackForwardListItem> m_targetItem;
>+        unsigned m_tickCallbackID { 0 };
>+
>+        Seconds m_prevTime;
>+        double m_velocity { 0 };
>+
>+        Seconds m_startTime;
>+        Seconds m_endTime;
>+
>+        float m_progress { 0 };
>+        float m_startProgress { 0 };
>+        float m_endProgress { 0 };
>+        bool m_cancelled { false };
>+
>+        ViewGestureController& m_viewGestureController;
>+        WebPageProxy& m_webPageProxy;
>+    };
>+
>+    SwipeProgressTracker m_swipeProgressTracker;
>+
>+    RefPtr<cairo_pattern_t> m_currentSwipeSnapshotPattern;
>+#endif
>+
>+    bool m_isConnectedToProcess { false };
>+
>+    SnapshotRemovalTracker m_snapshotRemovalTracker;
>+    WTF::Function<void()> m_loadCallback;
>+};
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/ViewGestureController.messages.in b/Source/WebKit/UIProcess/ViewGestureController.messages.in
>new file mode 100644
>index 0000000000000000000000000000000000000000..e9c21a5b4fff6382da6fb139c17c0140b212b90c
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/ViewGestureController.messages.in
>@@ -0,0 +1,32 @@
>+# Copyright (C) 2013 Apple Inc. All rights reserved.
>+#
>+# Redistribution and use in source and binary forms, with or without
>+# modification, are permitted provided that the following conditions
>+# are met:
>+# 1.  Redistributions of source code must retain the above copyright
>+#     notice, this list of conditions and the following disclaimer.
>+# 2.  Redistributions in binary form must reproduce the above copyright
>+#     notice, this list of conditions and the following disclaimer in the
>+#     documentation and/or other materials provided with the distribution.
>+#
>+# THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND
>+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
>+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
>+# DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR
>+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
>+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
>+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
>+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
>+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
>+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>+
>+messages -> ViewGestureController {
>+#if PLATFORM(MAC)
>+    DidCollectGeometryForMagnificationGesture(WebCore::FloatRect visibleContentBounds, bool frameHandlesMagnificationGesture)
>+    DidCollectGeometryForSmartMagnificationGesture(WebCore::FloatPoint origin, WebCore::FloatRect renderRect, WebCore::FloatRect visibleContentBounds, bool fitEntireRect, double viewportMinimumScale, double viewportMaximumScale)
>+#endif
>+
>+#if !PLATFORM(IOS_FAMILY)
>+    DidHitRenderTreeSizeThreshold()
>+#endif
>+}
>diff --git a/Source/WebKit/UIProcess/ViewSnapshotStore.cpp b/Source/WebKit/UIProcess/ViewSnapshotStore.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..cc78fa307823026a1d5a8def4ffb2bfef54d6d7b
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/ViewSnapshotStore.cpp
>@@ -0,0 +1,115 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "ViewSnapshotStore.h"
>+
>+#include "WebBackForwardList.h"
>+#include "WebPageProxy.h"
>+#include <wtf/NeverDestroyed.h>
>+
>+#if PLATFORM(IOS_FAMILY)
>+static const size_t maximumSnapshotCacheSize = 50 * (1024 * 1024);
>+#else
>+static const size_t maximumSnapshotCacheSize = 400 * (1024 * 1024);
>+#endif
>+
>+namespace WebKit {
>+using namespace WebCore;
>+
>+ViewSnapshotStore::ViewSnapshotStore()
>+{
>+}
>+
>+ViewSnapshotStore::~ViewSnapshotStore()
>+{
>+    discardSnapshotImages();
>+}
>+
>+ViewSnapshotStore& ViewSnapshotStore::singleton()
>+{
>+    static NeverDestroyed<ViewSnapshotStore> store;
>+    return store;
>+}
>+
>+void ViewSnapshotStore::didAddImageToSnapshot(ViewSnapshot& snapshot)
>+{
>+    bool isNewEntry = m_snapshotsWithImages.add(&snapshot).isNewEntry;
>+    ASSERT_UNUSED(isNewEntry, isNewEntry);
>+    m_snapshotCacheSize += snapshot.imageSizeInBytes();
>+}
>+
>+void ViewSnapshotStore::willRemoveImageFromSnapshot(ViewSnapshot& snapshot)
>+{
>+    bool removed = m_snapshotsWithImages.remove(&snapshot);
>+    ASSERT_UNUSED(removed, removed);
>+    m_snapshotCacheSize -= snapshot.imageSizeInBytes();
>+}
>+
>+void ViewSnapshotStore::pruneSnapshots(WebPageProxy& webPageProxy)
>+{
>+    if (m_snapshotCacheSize <= maximumSnapshotCacheSize)
>+        return;
>+
>+    ASSERT(!m_snapshotsWithImages.isEmpty());
>+
>+    // FIXME: We have enough information to do smarter-than-LRU eviction (making use of the back-forward lists, etc.)
>+
>+    m_snapshotsWithImages.first()->clearImage();
>+}
>+
>+void ViewSnapshotStore::recordSnapshot(WebPageProxy& webPageProxy, WebBackForwardListItem& item)
>+{
>+    if (webPageProxy.isShowingNavigationGestureSnapshot())
>+        return;
>+
>+    pruneSnapshots(webPageProxy);
>+
>+    webPageProxy.willRecordNavigationSnapshot(item);
>+
>+    auto snapshot = webPageProxy.takeViewSnapshot();
>+    if (!snapshot)
>+        return;
>+
>+    snapshot->setRenderTreeSize(webPageProxy.renderTreeSize());
>+    snapshot->setDeviceScaleFactor(webPageProxy.deviceScaleFactor());
>+    snapshot->setBackgroundColor(webPageProxy.pageExtendedBackgroundColor());
>+    snapshot->setViewScrollPosition(WebCore::roundedIntPoint(webPageProxy.viewScrollPosition()));
>+
>+    item.setSnapshot(WTFMove(snapshot));
>+}
>+
>+void ViewSnapshotStore::discardSnapshotImages()
>+{
>+    while (!m_snapshotsWithImages.isEmpty())
>+        m_snapshotsWithImages.first()->clearImage();
>+}
>+
>+ViewSnapshot::~ViewSnapshot()
>+{
>+    clearImage();
>+}
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/ViewSnapshotStore.h b/Source/WebKit/UIProcess/ViewSnapshotStore.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..20024a587ae3d4ed1111efafe29a01415c38c5e8
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/ViewSnapshotStore.h
>@@ -0,0 +1,174 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#pragma once
>+
>+#include <WebCore/Color.h>
>+#include <WebCore/IntPoint.h>
>+#include <WebCore/IntSize.h>
>+#include <wtf/ListHashSet.h>
>+#include <wtf/Noncopyable.h>
>+#include <wtf/RefCounted.h>
>+#include <wtf/text/WTFString.h>
>+
>+#if PLATFORM(COCOA)
>+#include <WebCore/IOSurface.h>
>+#endif
>+
>+#if PLATFORM(GTK)
>+#include <WebCore/RefPtrCairo.h>
>+#endif
>+
>+#if PLATFORM(COCOA)
>+#if !defined(__OBJC__)
>+typedef struct objc_object *id;
>+#endif
>+
>+OBJC_CLASS CAContext;
>+
>+#if HAVE(IOSURFACE)
>+namespace WebCore {
>+class IOSurface;
>+}
>+#endif
>+#endif
>+
>+namespace WebKit {
>+
>+class ViewSnapshotStore;
>+class WebBackForwardListItem;
>+class WebPageProxy;
>+
>+class ViewSnapshot : public RefCounted<ViewSnapshot> {
>+public:
>+#if PLATFORM(COCOA)
>+#if HAVE(IOSURFACE)
>+    static Ref<ViewSnapshot> create(std::unique_ptr<WebCore::IOSurface>);
>+#else
>+    static Ref<ViewSnapshot> create(uint32_t slotID, WebCore::IntSize, size_t imageSizeInBytes);
>+#endif
>+#elif PLATFORM(GTK)
>+    static Ref<ViewSnapshot> create(RefPtr<cairo_surface_t>&&);
>+#endif
>+
>+    ~ViewSnapshot();
>+
>+    void clearImage();
>+    bool hasImage() const;
>+#if PLATFORM(COCOA)
>+    id asLayerContents();
>+    RetainPtr<CGImageRef> asImageForTesting();
>+#endif
>+
>+    void setRenderTreeSize(uint64_t renderTreeSize) { m_renderTreeSize = renderTreeSize; }
>+    uint64_t renderTreeSize() const { return m_renderTreeSize; }
>+
>+    void setBackgroundColor(WebCore::Color color) { m_backgroundColor = color; }
>+    WebCore::Color backgroundColor() const { return m_backgroundColor; }
>+
>+    void setViewScrollPosition(WebCore::IntPoint scrollPosition) { m_viewScrollPosition = scrollPosition; }
>+    WebCore::IntPoint viewScrollPosition() const { return m_viewScrollPosition; }
>+
>+    void setDeviceScaleFactor(float deviceScaleFactor) { m_deviceScaleFactor = deviceScaleFactor; }
>+    float deviceScaleFactor() const { return m_deviceScaleFactor; }
>+
>+#if PLATFORM(COCOA)
>+#if HAVE(IOSURFACE)
>+    WebCore::IOSurface* surface() const { return m_surface.get(); }
>+
>+    size_t imageSizeInBytes() const { return m_surface ? m_surface->totalBytes() : 0; }
>+    WebCore::IntSize size() const { return m_surface ? m_surface->size() : WebCore::IntSize(); }
>+
>+    void setSurface(std::unique_ptr<WebCore::IOSurface>);
>+
>+    WebCore::IOSurface::SurfaceState setVolatile(bool);
>+#else
>+    WebCore::IntSize size() const { return m_size; }
>+    size_t imageSizeInBytes() const { return m_imageSizeInBytes; }
>+#endif
>+#elif PLATFORM(GTK)
>+    cairo_surface_t* surface() const { return m_surface.get(); }
>+
>+    size_t imageSizeInBytes() const;
>+    WebCore::IntSize size() const;
>+#endif
>+
>+private:
>+#if PLATFORM(COCOA)
>+#if HAVE(IOSURFACE)
>+    explicit ViewSnapshot(std::unique_ptr<WebCore::IOSurface>);
>+
>+    std::unique_ptr<WebCore::IOSurface> m_surface;
>+#else
>+    explicit ViewSnapshot(uint32_t slotID, WebCore::IntSize, size_t imageSizeInBytes);
>+
>+    uint32_t m_slotID;
>+    size_t m_imageSizeInBytes;
>+    WebCore::IntSize m_size;
>+#endif
>+#elif PLATFORM(GTK)
>+    explicit ViewSnapshot(RefPtr<cairo_surface_t>&&);
>+
>+    RefPtr<cairo_surface_t> m_surface { nullptr };
>+#endif
>+
>+    uint64_t m_renderTreeSize;
>+    float m_deviceScaleFactor;
>+    WebCore::Color m_backgroundColor;
>+    WebCore::IntPoint m_viewScrollPosition; // Scroll position at snapshot time. Integral to make comparison reliable.
>+};
>+
>+class ViewSnapshotStore {
>+    WTF_MAKE_NONCOPYABLE(ViewSnapshotStore);
>+    friend class ViewSnapshot;
>+public:
>+    ViewSnapshotStore();
>+    ~ViewSnapshotStore();
>+
>+    static ViewSnapshotStore& singleton();
>+
>+    void recordSnapshot(WebPageProxy&, WebBackForwardListItem&);
>+
>+    void discardSnapshotImages();
>+
>+    void setDisableSnapshotVolatilityForTesting(bool disable) { m_disableSnapshotVolatility = disable; }
>+    bool disableSnapshotVolatilityForTesting() const { return m_disableSnapshotVolatility; }
>+
>+#if !HAVE(IOSURFACE) && HAVE(CORE_ANIMATION_RENDER_SERVER)
>+    static CAContext *snapshottingContext();
>+#endif
>+
>+private:
>+    void didAddImageToSnapshot(ViewSnapshot&);
>+    void willRemoveImageFromSnapshot(ViewSnapshot&);
>+    void pruneSnapshots(WebPageProxy&);
>+
>+    size_t m_snapshotCacheSize { 0 };
>+
>+    ListHashSet<ViewSnapshot*> m_snapshotsWithImages;
>+    bool m_disableSnapshotVolatility { false };
>+};
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/WebBackForwardList.cpp b/Source/WebKit/UIProcess/WebBackForwardList.cpp
>index f2d5a162c407213ca829164d94ea265b9dd1c5c8..7564f3c36cac6dee305a8d9625d30d10c690b8ac 100644
>--- a/Source/WebKit/UIProcess/WebBackForwardList.cpp
>+++ b/Source/WebKit/UIProcess/WebBackForwardList.cpp
>@@ -468,7 +468,7 @@ void WebBackForwardList::didRemoveItem(WebBackForwardListItem& backForwardListIt
>     m_page->backForwardRemovedItem(backForwardListItem.itemID());
> 
>     backForwardListItem.setSuspendedPage(nullptr);
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     backForwardListItem.setSnapshot(nullptr);
> #endif
> }
>diff --git a/Source/WebKit/UIProcess/WebMemoryPressureHandler.cpp b/Source/WebKit/UIProcess/WebMemoryPressureHandler.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..70677735545ade8b274b875792f5b18752ffa3d0
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/WebMemoryPressureHandler.cpp
>@@ -0,0 +1,47 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "WebMemoryPressureHandler.h"
>+
>+#include "ViewSnapshotStore.h"
>+#include "WebProcessPool.h"
>+#include <wtf/MemoryPressureHandler.h>
>+
>+namespace WebKit {
>+
>+void installMemoryPressureHandler()
>+{
>+    auto& memoryPressureHandler = MemoryPressureHandler::singleton();
>+    memoryPressureHandler.setLowMemoryHandler([] (Critical critical, Synchronous) {
>+        ViewSnapshotStore::singleton().discardSnapshotImages();
>+
>+        for (auto* processPool : WebProcessPool::allProcessPools())
>+            processPool->handleMemoryPressureWarning(critical);
>+    });
>+    memoryPressureHandler.install();
>+}
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/WebMemoryPressureHandler.h b/Source/WebKit/UIProcess/WebMemoryPressureHandler.h
>new file mode 100644
>index 0000000000000000000000000000000000000000..6855b0a8eb954871737af5ce4d978974607e9b8e
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/WebMemoryPressureHandler.h
>@@ -0,0 +1,32 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#pragma once
>+
>+namespace WebKit {
>+
>+void installMemoryPressureHandler();
>+
>+}
>diff --git a/Source/WebKit/UIProcess/WebPageProxy.cpp b/Source/WebKit/UIProcess/WebPageProxy.cpp
>index 70a0970e8f987b8168744e2ac64e35ac1715278f..b5151c73a14aaee73f22817566a015783d77ef15 100644
>--- a/Source/WebKit/UIProcess/WebPageProxy.cpp
>+++ b/Source/WebKit/UIProcess/WebPageProxy.cpp
>@@ -189,12 +189,15 @@
> #include "TouchBarMenuItemData.h"
> #include "VideoFullscreenManagerProxy.h"
> #include "VideoFullscreenManagerProxyMessages.h"
>-#include "ViewSnapshotStore.h"
> #include <WebCore/RunLoopObserver.h>
> #include <WebCore/TextIndicatorWindow.h>
> #include <wtf/MachSendRight.h>
> #endif
> 
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>+#include "ViewSnapshotStore.h"
>+#endif
>+
> #if PLATFORM(GTK)
> #include "WebSelectionData.h"
> #endif
>@@ -1348,7 +1351,7 @@ void WebPageProxy::recordNavigationSnapshot(WebBackForwardListItem& item)
>     if (!m_shouldRecordNavigationSnapshots)
>         return;
> 
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     ViewSnapshotStore::singleton().recordSnapshot(*this, item);
> #else
>     UNUSED_PARAM(item);
>@@ -7470,7 +7473,7 @@ void WebPageProxy::setEditableElementIsFocused(bool editableElementIsFocused)
> 
> #endif // PLATFORM(MAC)
> 
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
> RefPtr<ViewSnapshot> WebPageProxy::takeViewSnapshot()
> {
>     return pageClient().takeViewSnapshot();
>diff --git a/Source/WebKit/UIProcess/WebPageProxy.h b/Source/WebKit/UIProcess/WebPageProxy.h
>index 96cf862606c0f25dcce198b563ff3087b384d959..d99c2ada4b4d6c3a36734f434ed9555e48a8c0bc 100644
>--- a/Source/WebKit/UIProcess/WebPageProxy.h
>+++ b/Source/WebKit/UIProcess/WebPageProxy.h
>@@ -1230,7 +1230,7 @@ public:
>     void recordNavigationSnapshot(WebBackForwardListItem&);
>     void requestFocusedElementInformation(Function<void(const FocusedElementInformation&, CallbackBase::Error)>&&);
> 
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     RefPtr<ViewSnapshot> takeViewSnapshot();
> #endif
> 
>diff --git a/Source/WebKit/UIProcess/gtk/ViewGestureControllerGtk.cpp b/Source/WebKit/UIProcess/gtk/ViewGestureControllerGtk.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..4af6ef0b5716d6e99daf6d79522dcd8e2d5fbe77
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/gtk/ViewGestureControllerGtk.cpp
>@@ -0,0 +1,349 @@
>+/*
>+ * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "ViewGestureController.h"
>+
>+#include "DrawingAreaProxy.h"
>+#include "WebBackForwardList.h"
>+
>+namespace WebKit {
>+using namespace WebCore;
>+
>+static const Seconds swipeMinAnimationDuration = 100_ms;
>+static const Seconds swipeMaxAnimationDuration = 400_ms;
>+
>+static const double swipeOverlayShadowOpacity = 0.06;
>+static const double swipeOverlayDimmingOpacity = 0.12;
>+static const double swipeOverlayShadowWidth = 81;
>+static const double swipeOverlayShadowGradientOffsets[] = { 0, 0.03125, 0.0625, 0.0938, 0.125, 0.1875, 0.25, 0.375, 0.4375, 0.5, 0.5625, 0.625, 0.6875, 0.75, 0.875, 1. };
>+static const double swipeOverlayShadowGradientAlpha[] = { 1, 0.99, 0.98, 0.95, 0.92, 0.82, 0.71, 0.46, 0.35, 0.25, 0.17, 0.11, 0.07, 0.04, 0.01, 0. };
>+
>+static bool isEventStop(GdkEventScroll* event)
>+{
>+#if GTK_CHECK_VERSION(3, 20, 0)
>+    return event->is_stop;
>+#else
>+    return !event->delta_x && !event->delta_y;
>+#endif
>+}
>+
>+void ViewGestureController::platformTeardown()
>+{
>+    m_swipeProgressTracker.reset();
>+
>+    if (m_activeGestureType == ViewGestureType::Swipe)
>+        removeSwipeSnapshot();
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanStartSwipe(GdkEventScroll*)
>+{
>+    return true;
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanEndSwipe(GdkEventScroll* event)
>+{
>+    return isEventStop(event);
>+}
>+
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanInfluenceSwipe(GdkEventScroll* event)
>+{
>+    GdkDevice* device = gdk_event_get_source_device(reinterpret_cast<GdkEvent*>(event));
>+    GdkInputSource source = gdk_device_get_source(device);
>+
>+    // FIXME: Should it maybe be allowed on mice/trackpoints as well? The GDK_SCROLL_SMOOTH
>+    // requirement already filters out most mice, and it works pretty well on a trackpoint
>+    return event->direction == GDK_SCROLL_SMOOTH && source == GDK_SOURCE_TOUCHPAD;
>+}
>+
>+FloatSize ViewGestureController::PendingSwipeTracker::scrollEventGetScrollingDeltas(GdkEventScroll* event)
>+{
>+    // GdkEventScroll deltas are inverted compared to NSEvent, so invert them again
>+    return -FloatSize(event->delta_x, event->delta_y) * Scrollbar::pixelsPerLineStep();
>+}
>+
>+bool ViewGestureController::handleScrollWheelEvent(GdkEventScroll* event)
>+{
>+    return m_swipeProgressTracker.handleEvent(event) || m_pendingSwipeTracker.handleEvent(event);
>+}
>+
>+void ViewGestureController::trackSwipeGesture(PlatformScrollEvent event, SwipeDirection direction, RefPtr<WebBackForwardListItem> targetItem)
>+{
>+    m_swipeProgressTracker.startTracking(WTFMove(targetItem), direction);
>+    m_swipeProgressTracker.handleEvent(event);
>+}
>+
>+ViewGestureController::SwipeProgressTracker::SwipeProgressTracker(WebPageProxy& webPageProxy, ViewGestureController& viewGestureController)
>+    : m_viewGestureController(viewGestureController)
>+    , m_webPageProxy(webPageProxy)
>+{
>+}
>+
>+void ViewGestureController::SwipeProgressTracker::startTracking(RefPtr<WebBackForwardListItem>&& targetItem, SwipeDirection direction)
>+{
>+    if (m_state != State::None)
>+        return;
>+
>+    m_targetItem = targetItem;
>+    m_direction = direction;
>+    m_state = State::Pending;
>+}
>+
>+void ViewGestureController::SwipeProgressTracker::reset()
>+{
>+    m_targetItem = nullptr;
>+    m_state = State::None;
>+
>+    if (m_tickCallbackID) {
>+        GtkWidget* widget = m_webPageProxy.viewWidget();
>+        gtk_widget_remove_tick_callback(widget, m_tickCallbackID);
>+        m_tickCallbackID = 0;
>+    }
>+
>+    m_progress = 0;
>+    m_startProgress = 0;
>+    m_endProgress = 0;
>+
>+    m_startTime = 0_ms;
>+    m_endTime = 0_ms;
>+    m_prevTime = 0_ms;
>+    m_velocity = 0;
>+    m_cancelled = false;
>+}
>+
>+bool ViewGestureController::SwipeProgressTracker::handleEvent(GdkEventScroll* event)
>+{
>+    if (m_state == State::Pending) {
>+        m_viewGestureController.beginSwipeGesture(m_targetItem.get(), m_direction);
>+        m_state = State::Scrolling;
>+    }
>+
>+    // Don't allow scrolling during animation
>+    if (m_state == State::Animating)
>+        return true;
>+
>+    if (m_state != State::Scrolling)
>+        return false;
>+
>+    if (isEventStop(event)) {
>+        startAnimation();
>+        return false;
>+    }
>+
>+    Seconds time = Seconds::fromMilliseconds(event->time);
>+    m_velocity = -event->delta_x / (time - m_prevTime).milliseconds();
>+
>+    m_prevTime = time;
>+    m_progress -= event->delta_x / Scrollbar::pixelsPerLineStep();
>+
>+    bool swipingLeft = m_viewGestureController.isPhysicallySwipingLeft(m_direction);
>+    float maxProgress = swipingLeft ? 1 : 0;
>+    float minProgress = !swipingLeft ? -1 : 0;
>+    m_progress = clampTo<float>(m_progress, minProgress, maxProgress);
>+
>+    m_viewGestureController.handleSwipeGesture(m_targetItem.get(), m_progress, m_direction);
>+
>+    return true;
>+}
>+
>+void ViewGestureController::SwipeProgressTracker::startAnimation()
>+{
>+    bool swipingLeft = m_viewGestureController.isPhysicallySwipingLeft(m_direction);
>+    m_cancelled = swipingLeft ? (m_velocity <= 0) : (m_velocity >= 0);
>+
>+    m_state = State::Animating;
>+    m_viewGestureController.willEndSwipeGesture(*m_targetItem, m_cancelled);
>+
>+    m_startProgress = m_progress;
>+    if (m_cancelled)
>+        m_endProgress = 0;
>+    else
>+        m_endProgress = swipingLeft ? 1 : -1;
>+
>+    Seconds duration = Seconds::fromMilliseconds(std::abs((m_progress - m_endProgress) / m_velocity) * Scrollbar::pixelsPerLineStep());
>+    duration = std::min(std::max(duration, swipeMinAnimationDuration), swipeMaxAnimationDuration);
>+
>+    GtkWidget* widget = m_webPageProxy.viewWidget();
>+    m_startTime = Seconds::fromMicroseconds(gdk_frame_clock_get_frame_time(gtk_widget_get_frame_clock(widget)));
>+    m_endTime = m_startTime + duration;
>+
>+    m_tickCallbackID = gtk_widget_add_tick_callback(widget, [](GtkWidget*, GdkFrameClock* frameClock, gpointer userData) -> gboolean {
>+        auto* tracker = static_cast<SwipeProgressTracker*>(userData);
>+        return tracker->onAnimationTick(frameClock);
>+    }, this, nullptr);
>+}
>+
>+static inline double easeOutCubic(double t)
>+{
>+    double p = t - 1;
>+    return p * p * p + 1;
>+}
>+
>+gboolean ViewGestureController::SwipeProgressTracker::onAnimationTick(GdkFrameClock* frameClock)
>+{
>+    ASSERT(m_state == State::Animating);
>+    ASSERT(m_endTime > m_startTime);
>+
>+    Seconds frameTime = Seconds::fromMicroseconds(gdk_frame_clock_get_frame_time(frameClock));
>+
>+    double animationProgress = (frameTime - m_startTime) / (m_endTime - m_startTime);
>+    if (animationProgress > 1)
>+        animationProgress = 1;
>+
>+    m_progress = m_startProgress + (m_endProgress - m_startProgress) * easeOutCubic(animationProgress);
>+
>+    m_viewGestureController.handleSwipeGesture(m_targetItem.get(), m_progress, m_direction);
>+    if (frameTime >= m_endTime) {
>+        m_tickCallbackID = 0;
>+        endAnimation();
>+        return G_SOURCE_REMOVE;
>+    }
>+
>+    return G_SOURCE_CONTINUE;
>+}
>+
>+void ViewGestureController::SwipeProgressTracker::endAnimation()
>+{
>+    m_viewGestureController.endSwipeGesture(m_targetItem.get(), m_cancelled);
>+}
>+
>+void ViewGestureController::beginSwipeGesture(WebBackForwardListItem* targetItem, SwipeDirection direction)
>+{
>+    ASSERT(targetItem);
>+
>+    m_webPageProxy.navigationGestureDidBegin();
>+
>+    willBeginGesture(ViewGestureType::Swipe);
>+
>+    if (auto* snapshot = targetItem->snapshot()) {
>+        m_currentSwipeSnapshot = snapshot;
>+
>+        FloatSize viewSize(m_webPageProxy.viewSize());
>+        if (snapshot->hasImage() && shouldUseSnapshotForSize(*snapshot, viewSize, 0))
>+            m_currentSwipeSnapshotPattern = adoptRef(cairo_pattern_create_for_surface(snapshot->surface()));
>+
>+        Color color = snapshot->backgroundColor();
>+        if (color.isValid()) {
>+            m_backgroundColorForCurrentSnapshot = color;
>+            if (!m_currentSwipeSnapshotPattern) {
>+                double red, green, blue, alpha;
>+                color.getRGBA(red, green, blue, alpha);
>+                m_currentSwipeSnapshotPattern = adoptRef(cairo_pattern_create_rgba(red, green, blue, alpha));
>+            }
>+        }
>+    }
>+
>+    if (!m_currentSwipeSnapshotPattern)
>+        m_currentSwipeSnapshotPattern = adoptRef(cairo_pattern_create_rgb(1, 1, 1));
>+}
>+
>+void ViewGestureController::handleSwipeGesture(WebBackForwardListItem*, double, SwipeDirection)
>+{
>+    gtk_widget_queue_draw(m_webPageProxy.viewWidget());
>+}
>+
>+void ViewGestureController::draw(cairo_t* cr, cairo_pattern_t* pageGroup)
>+{
>+    bool swipingLeft = isPhysicallySwipingLeft(m_swipeProgressTracker.direction());
>+    float progress = m_swipeProgressTracker.progress();
>+
>+    double width = m_webPageProxy.drawingArea()->size().width();
>+    double height = m_webPageProxy.drawingArea()->size().height();
>+
>+    double swipingLayerOffset = (swipingLeft ? 0 : width) + floor(width * progress);
>+
>+    double dimmingProgress = swipingLeft ? 1 - progress : -progress;
>+
>+    double remainingSwipeDistance = dimmingProgress * width;
>+    double shadowFadeDistance = swipeOverlayShadowWidth;
>+
>+    double shadowOpacity = swipeOverlayShadowOpacity;
>+    if (remainingSwipeDistance < shadowFadeDistance)
>+        shadowOpacity = (remainingSwipeDistance / shadowFadeDistance) * swipeOverlayShadowOpacity;
>+
>+    RefPtr<cairo_pattern_t> shadowPattern = adoptRef(cairo_pattern_create_linear(0, 0, -swipeOverlayShadowWidth, 0));
>+    for (int i = 0; i < 16; i++) {
>+        double offset = swipeOverlayShadowGradientOffsets[i];
>+        double alpha = swipeOverlayShadowGradientAlpha[i] * shadowOpacity;
>+        cairo_pattern_add_color_stop_rgba(shadowPattern.get(), offset, 0, 0, 0, alpha);
>+    }
>+
>+    cairo_save(cr);
>+
>+    cairo_rectangle(cr, 0, 0, swipingLayerOffset, height);
>+    cairo_set_source(cr, swipingLeft ? m_currentSwipeSnapshotPattern.get() : pageGroup);
>+    cairo_fill_preserve(cr);
>+
>+    cairo_set_source_rgba(cr, 0, 0, 0, dimmingProgress * swipeOverlayDimmingOpacity);
>+    cairo_fill(cr);
>+
>+    cairo_translate(cr, swipingLayerOffset, 0);
>+
>+    if (progress) {
>+        cairo_rectangle(cr, -swipeOverlayShadowWidth, 0, swipeOverlayShadowWidth, height);
>+        cairo_set_source(cr, shadowPattern.get());
>+        cairo_fill(cr);
>+    }
>+
>+    cairo_rectangle(cr, 0, 0, width - swipingLayerOffset, height);
>+    cairo_set_source(cr, swipingLeft ? pageGroup : m_currentSwipeSnapshotPattern.get());
>+    cairo_fill(cr);
>+
>+    cairo_restore(cr);
>+}
>+
>+void ViewGestureController::removeSwipeSnapshot()
>+{
>+    m_snapshotRemovalTracker.reset();
>+
>+    m_hasOutstandingRepaintRequest = false;
>+
>+    if (m_activeGestureType != ViewGestureType::Swipe)
>+        return;
>+
>+    m_currentSwipeSnapshotPattern = nullptr;
>+
>+    m_currentSwipeSnapshot = nullptr;
>+
>+    m_webPageProxy.navigationGestureSnapshotWasRemoved();
>+
>+    m_backgroundColorForCurrentSnapshot = Color();
>+
>+    didEndGesture();
>+
>+    m_swipeProgressTracker.reset();
>+}
>+
>+bool ViewGestureController::beginSimulatedSwipeInDirectionForTesting(SwipeDirection)
>+{
>+    return false;
>+}
>+
>+bool ViewGestureController::completeSimulatedSwipeInDirectionForTesting(SwipeDirection)
>+{
>+    return false;
>+}
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/gtk/ViewSnapshotStoreGtk.cpp b/Source/WebKit/UIProcess/gtk/ViewSnapshotStoreGtk.cpp
>new file mode 100644
>index 0000000000000000000000000000000000000000..6d2baad688ea20485ed09f32ddcbc6cc9e27b991
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/gtk/ViewSnapshotStoreGtk.cpp
>@@ -0,0 +1,85 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#include "config.h"
>+#include "ViewSnapshotStore.h"
>+
>+#include <WebCore/CairoUtilities.h>
>+
>+namespace WebKit {
>+using namespace WebCore;
>+
>+Ref<ViewSnapshot> ViewSnapshot::create(RefPtr<cairo_surface_t>&& surface)
>+{
>+    return adoptRef(*new ViewSnapshot(WTFMove(surface)));
>+}
>+
>+ViewSnapshot::ViewSnapshot(RefPtr<cairo_surface_t>&& surface)
>+    : m_surface(WTFMove(surface))
>+{
>+    if (hasImage())
>+        ViewSnapshotStore::singleton().didAddImageToSnapshot(*this);
>+}
>+
>+bool ViewSnapshot::hasImage() const
>+{
>+    return !!m_surface;
>+}
>+
>+void ViewSnapshot::clearImage()
>+{
>+    if (!hasImage())
>+        return;
>+
>+    ViewSnapshotStore::singleton().willRemoveImageFromSnapshot(*this);
>+
>+    m_surface = nullptr;
>+}
>+
>+size_t ViewSnapshot::imageSizeInBytes() const
>+{
>+    if (!m_surface)
>+        return 0;
>+
>+    cairo_surface_t* surface = m_surface.get();
>+    int stride = cairo_image_surface_get_stride(surface);
>+    int height = cairo_image_surface_get_width(surface);
>+
>+    return stride * height;
>+}
>+
>+WebCore::IntSize ViewSnapshot::size() const
>+{
>+    if (!m_surface)
>+        return { };
>+
>+    cairo_surface_t* surface = m_surface.get();
>+    int width = cairo_image_surface_get_width(surface);
>+    int height = cairo_image_surface_get_height(surface);
>+
>+    return { width, height };
>+}
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/gtk/WebProcessPoolGtk.cpp b/Source/WebKit/UIProcess/gtk/WebProcessPoolGtk.cpp
>index 6b2357404e03ae3021ae880b63a8cec0ee86f0f6..5127d3af6edd7804e31912d5c6909996c6fc2678 100644
>--- a/Source/WebKit/UIProcess/gtk/WebProcessPoolGtk.cpp
>+++ b/Source/WebKit/UIProcess/gtk/WebProcessPoolGtk.cpp
>@@ -31,6 +31,7 @@
> #include "APIProcessPoolConfiguration.h"
> #include "Logging.h"
> #include "WebCookieManagerProxy.h"
>+#include "WebMemoryPressureHandler.h"
> #include "WebProcessCreationParameters.h"
> #include "WebProcessMessages.h"
> #include <JavaScriptCore/RemoteInspectorServer.h>
>@@ -67,6 +68,12 @@ static bool initializeRemoteInspectorServer(const char* address)
> }
> #endif
> 
>+static bool memoryPressureMonitorDisabled()
>+{
>+    static const char* disableMemoryPressureMonitor = getenv("WEBKIT_DISABLE_MEMORY_PRESSURE_MONITOR");
>+    return disableMemoryPressureMonitor && !strcmp(disableMemoryPressureMonitor, "1");
>+}
>+
> void WebProcessPool::platformInitialize()
> {
> #if ENABLE(REMOTE_INSPECTOR)
>@@ -75,6 +82,9 @@ void WebProcessPool::platformInitialize()
>             g_unsetenv("WEBKIT_INSPECTOR_SERVER");
>     }
> #endif
>+
>+    if (!memoryPressureMonitorDisabled())
>+        installMemoryPressureHandler();
> }
> 
> void WebProcessPool::platformInitializeWebProcess(WebProcessCreationParameters& parameters)
>@@ -87,8 +97,7 @@ void WebProcessPool::platformInitializeWebProcess(WebProcessCreationParameters&
>     if (forceComplexText && !strcmp(forceComplexText, "0"))
>         parameters.shouldAlwaysUseComplexTextCodePath = m_alwaysUsesComplexTextCodePath;
> 
>-    const char* disableMemoryPressureMonitor = getenv("WEBKIT_DISABLE_MEMORY_PRESSURE_MONITOR");
>-    if (disableMemoryPressureMonitor && !strcmp(disableMemoryPressureMonitor, "1"))
>+    if (memoryPressureMonitorDisabled())
>         parameters.shouldSuppressMemoryPressureHandler = true;
> 
> #if USE(GSTREAMER)
>diff --git a/Source/WebKit/UIProcess/mac/ViewGestureControllerMac.mm b/Source/WebKit/UIProcess/mac/ViewGestureControllerMac.mm
>index 401f6e72c4a678b0b1eedefe966bc11d58c49ad0..872e298f20af12803576da5499aae5b8c75c7996 100644
>--- a/Source/WebKit/UIProcess/mac/ViewGestureControllerMac.mm
>+++ b/Source/WebKit/UIProcess/mac/ViewGestureControllerMac.mm
>@@ -28,7 +28,6 @@
> 
> #if PLATFORM(MAC)
> 
>-#import "APINavigation.h"
> #import "DrawingAreaProxy.h"
> #import "FrameLoadState.h"
> #import "Logging.h"
>@@ -66,11 +65,6 @@ static const double swipeOverlayShadowOpacity = 0.06;
> static const double swipeOverlayDimmingOpacity = 0.12;
> static const CGFloat swipeOverlayShadowWidth = 81;
> 
>-static const CGFloat minimumHorizontalSwipeDistance = 15;
>-static const float minimumScrollEventRatioForSwipe = 0.5;
>-
>-static const float swipeSnapshotRemovalRenderTreeSizeTargetFraction = 0.5;
>-
> @interface WKSwipeCancellationTracker : NSObject {
> @private
>     BOOL _isCancelled;
>@@ -265,46 +259,24 @@ void ViewGestureController::didCollectGeometryForSmartMagnificationGesture(Float
>     m_lastMagnificationGestureWasSmartMagnification = true;
> }
> 
>-static bool scrollEventCanInfluenceSwipe(NSEvent *event)
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanStartSwipe(NSEvent *event)
> {
>-    return event.hasPreciseScrollingDeltas && [NSEvent isSwipeTrackingFromScrollEventsEnabled];
>+    return event.phase == NSEventPhaseBegan;
> }
> 
>-static bool deltaShouldCancelSwipe(float x, float y)
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanEndSwipe(NSEvent *event)
> {
>-    return std::abs(y) >= std::abs(x) * minimumScrollEventRatioForSwipe;
>+    return event.phase == NSEventPhaseEnded;
> }
> 
>-ViewGestureController::PendingSwipeTracker::PendingSwipeTracker(WebPageProxy& webPageProxy, ViewGestureController& viewGestureController)
>-    : m_viewGestureController(viewGestureController)
>-    , m_webPageProxy(webPageProxy)
>+bool ViewGestureController::PendingSwipeTracker::scrollEventCanInfluenceSwipe(NSEvent *event)
> {
>+    return event.hasPreciseScrollingDeltas && [NSEvent isSwipeTrackingFromScrollEventsEnabled];
> }
> 
>-bool ViewGestureController::PendingSwipeTracker::scrollEventCanBecomeSwipe(NSEvent *event, ViewGestureController::SwipeDirection& potentialSwipeDirection)
>+FloatSize ViewGestureController::PendingSwipeTracker::scrollEventGetScrollingDeltas(NSEvent *event)
> {
>-    if (event.phase != NSEventPhaseBegan)
>-        return false;
>-
>-    if (!scrollEventCanInfluenceSwipe(event))
>-        return false;
>-
>-    if (deltaShouldCancelSwipe(event.scrollingDeltaX, event.scrollingDeltaY))
>-        return false;
>-
>-    bool isPinnedToLeft = m_shouldIgnorePinnedState || m_webPageProxy.isPinnedToLeftSide();
>-    bool isPinnedToRight = m_shouldIgnorePinnedState || m_webPageProxy.isPinnedToRightSide();
>-
>-    bool tryingToSwipeBack = event.scrollingDeltaX > 0 && isPinnedToLeft;
>-    bool tryingToSwipeForward = event.scrollingDeltaX < 0 && isPinnedToRight;
>-    if (m_webPageProxy.userInterfaceLayoutDirection() != WebCore::UserInterfaceLayoutDirection::LTR)
>-        std::swap(tryingToSwipeBack, tryingToSwipeForward);
>-    
>-    if (!tryingToSwipeBack && !tryingToSwipeForward)
>-        return false;
>-
>-    potentialSwipeDirection = tryingToSwipeBack ? SwipeDirection::Back : SwipeDirection::Forward;
>-    return m_viewGestureController.canSwipeInDirection(potentialSwipeDirection);
>+    return FloatSize(event.scrollingDeltaX, event.scrollingDeltaY);
> }
> 
> bool ViewGestureController::handleScrollWheelEvent(NSEvent *event)
>@@ -314,93 +286,12 @@ bool ViewGestureController::handleScrollWheelEvent(NSEvent *event)
>     return m_pendingSwipeTracker.handleEvent(event);
> }
> 
>-bool ViewGestureController::PendingSwipeTracker::handleEvent(NSEvent *event)
>-{
>-    if (event.phase == NSEventPhaseEnded) {
>-        reset("gesture ended");
>-        return false;
>-    }
>-
>-    if (m_state == State::None) {
>-        if (!scrollEventCanBecomeSwipe(event, m_direction))
>-            return false;
>-
>-        if (!m_shouldIgnorePinnedState && m_webPageProxy.willHandleHorizontalScrollEvents()) {
>-            m_state = State::WaitingForWebCore;
>-            LOG(ViewGestures, "Swipe Start Hysteresis - waiting for WebCore to handle event");
>-        }
>-    }
>-
>-    if (m_state == State::WaitingForWebCore)
>-        return false;
>-
>-    return tryToStartSwipe(event);
>-}
>-
>-void ViewGestureController::PendingSwipeTracker::eventWasNotHandledByWebCore(NSEvent *event)
>-{
>-    if (m_state != State::WaitingForWebCore)
>-        return;
>-
>-    LOG(ViewGestures, "Swipe Start Hysteresis - WebCore didn't handle event");
>-    m_state = State::None;
>-    m_cumulativeDelta = FloatSize();
>-    tryToStartSwipe(event);
>-}
>-
>-bool ViewGestureController::PendingSwipeTracker::tryToStartSwipe(NSEvent *event)
>-{
>-    ASSERT(m_state != State::WaitingForWebCore);
>-
>-    if (m_state == State::None) {
>-        SwipeDirection direction;
>-        if (!scrollEventCanBecomeSwipe(event, direction))
>-            return false;
>-    }
>-
>-    if (!scrollEventCanInfluenceSwipe(event))
>-        return false;
>-
>-    m_cumulativeDelta += FloatSize(event.scrollingDeltaX, event.scrollingDeltaY);
>-    LOG(ViewGestures, "Swipe Start Hysteresis - consumed event, cumulative delta (%0.2f, %0.2f)", m_cumulativeDelta.width(), m_cumulativeDelta.height());
>-
>-    if (deltaShouldCancelSwipe(m_cumulativeDelta.width(), m_cumulativeDelta.height())) {
>-        reset("cumulative delta became too vertical");
>-        return false;
>-    }
>-
>-    if (std::abs(m_cumulativeDelta.width()) >= minimumHorizontalSwipeDistance)
>-        m_viewGestureController.trackSwipeGesture(event, m_direction);
>-    else
>-        m_state = State::InsufficientMagnitude;
>-
>-    return true;
>-}
>-
>-void ViewGestureController::PendingSwipeTracker::reset(const char* resetReasonForLogging)
>+void ViewGestureController::trackSwipeGesture(PlatformScrollEvent event, SwipeDirection direction, RefPtr<WebBackForwardListItem> targetItem)
> {
>-    if (m_state != State::None)
>-        LOG(ViewGestures, "Swipe Start Hysteresis - reset; %s", resetReasonForLogging);
>-
>-    m_state = State::None;
>-    m_cumulativeDelta = FloatSize();
>-}
>-
>-void ViewGestureController::trackSwipeGesture(NSEvent *event, SwipeDirection direction)
>-{
>-    ASSERT(m_activeGestureType == ViewGestureType::None);
>-
>-    m_pendingSwipeTracker.reset("starting to track swipe");
>-
>-    m_webPageProxy.recordAutomaticNavigationSnapshot();
>-
>     BOOL swipingLeft = isPhysicallySwipingLeft(direction);
>     CGFloat maxProgress = swipingLeft ? 1 : 0;
>     CGFloat minProgress = !swipingLeft ? -1 : 0;
>-    RefPtr<WebBackForwardListItem> targetItem = (direction == SwipeDirection::Back) ? m_webPageProxy.backForwardList().backItem() : m_webPageProxy.backForwardList().forwardItem();
>-    if (!targetItem)
>-        return;
>-    
>+
>     __block bool swipeCancelled = false;
> 
>     ASSERT(!m_swipeCancellationTracker);
>@@ -425,11 +316,6 @@ void ViewGestureController::trackSwipeGesture(NSEvent *event, SwipeDirection dir
>     }];
> }
> 
>-void ViewGestureController::willEndSwipeGesture(WebBackForwardListItem& targetItem, bool cancelled)
>-{
>-    m_webPageProxy.navigationGestureWillEnd(!cancelled, targetItem);
>-}
>-
> FloatRect ViewGestureController::windowRelativeBoundsForCustomSwipeViews() const
> {
>     FloatRect swipeArea;
>@@ -488,20 +374,6 @@ CALayer *ViewGestureController::determineLayerAdjacentToSnapshotForParent(SwipeD
>     return layerAdjacentToSnapshot;
> }
> 
>-bool ViewGestureController::shouldUseSnapshotForSize(ViewSnapshot& snapshot, FloatSize swipeLayerSize, float topContentInset)
>-{
>-    float deviceScaleFactor = m_webPageProxy.deviceScaleFactor();
>-    if (snapshot.deviceScaleFactor() != deviceScaleFactor)
>-        return false;
>-
>-    FloatSize unobscuredSwipeLayerSizeInDeviceCoordinates = swipeLayerSize - FloatSize(0, topContentInset);
>-    unobscuredSwipeLayerSizeInDeviceCoordinates.scale(deviceScaleFactor);
>-    if (snapshot.size() != unobscuredSwipeLayerSizeInDeviceCoordinates)
>-        return false;
>-
>-    return true;
>-}
>-
> static bool layerGeometryFlippedToRoot(CALayer *layer)
> {
>     bool flipped = false;
>@@ -668,13 +540,6 @@ void ViewGestureController::beginSwipeGesture(WebBackForwardListItem* targetItem
>     }
> }
> 
>-bool ViewGestureController::isPhysicallySwipingLeft(SwipeDirection direction) const
>-{
>-    bool isLTR = m_webPageProxy.userInterfaceLayoutDirection() == WebCore::UserInterfaceLayoutDirection::LTR;
>-    bool isSwipingForward = direction == SwipeDirection::Forward;
>-    return isLTR != isSwipingForward;
>-}
>-
> void ViewGestureController::handleSwipeGesture(WebBackForwardListItem* targetItem, double progress, SwipeDirection direction)
> {
>     ASSERT(m_activeGestureType == ViewGestureType::Swipe);
>@@ -723,70 +588,6 @@ void ViewGestureController::didMoveSwipeSnapshotLayer()
>     m_didMoveSwipeSnapshotCallback(m_webPageProxy.boundsOfLayerInLayerBackedWindowCoordinates(m_swipeLayer.get()));
> }
> 
>-void ViewGestureController::endSwipeGesture(WebBackForwardListItem* targetItem, bool cancelled)
>-{
>-    ASSERT(m_activeGestureType == ViewGestureType::Swipe);
>-
>-    m_swipeCancellationTracker = nullptr;
>-
>-    if (cancelled) {
>-        removeSwipeSnapshot();
>-        m_webPageProxy.navigationGestureDidEnd(false, *targetItem);
>-        return;
>-    }
>-
>-    uint64_t renderTreeSize = 0;
>-    if (ViewSnapshot* snapshot = targetItem->snapshot())
>-        renderTreeSize = snapshot->renderTreeSize();
>-    auto renderTreeSizeThreshold = renderTreeSize * swipeSnapshotRemovalRenderTreeSizeTargetFraction;
>-
>-    m_webPageProxy.navigationGestureDidEnd(true, *targetItem);
>-    m_webPageProxy.goToBackForwardItem(*targetItem);
>-
>-    auto* currentItem = m_webPageProxy.backForwardList().currentItem();
>-    // The main frame will not be navigated so hide the snapshot right away.
>-    if (currentItem && currentItem->itemIsClone(*targetItem)) {
>-        removeSwipeSnapshot();
>-        return;
>-    }
>-
>-    SnapshotRemovalTracker::Events desiredEvents = SnapshotRemovalTracker::VisuallyNonEmptyLayout
>-        | SnapshotRemovalTracker::MainFrameLoad
>-        | SnapshotRemovalTracker::SubresourceLoads
>-        | SnapshotRemovalTracker::ScrollPositionRestoration;
>-
>-    if (renderTreeSizeThreshold) {
>-        desiredEvents |= SnapshotRemovalTracker::RenderTreeSizeThreshold;
>-        m_snapshotRemovalTracker.setRenderTreeSizeThreshold(renderTreeSizeThreshold);
>-    }
>-
>-    m_snapshotRemovalTracker.start(desiredEvents, [this] { this->forceRepaintIfNeeded(); });
>-
>-    // FIXME: Like on iOS, we should ensure that even if one of the timeouts fires,
>-    // we never show the old page content, instead showing the snapshot background color.
>-
>-    if (ViewSnapshot* snapshot = targetItem->snapshot())
>-        m_backgroundColorForCurrentSnapshot = snapshot->backgroundColor();
>-}
>-
>-void ViewGestureController::forceRepaintIfNeeded()
>-{
>-    if (m_activeGestureType != ViewGestureType::Swipe)
>-        return;
>-
>-    if (m_hasOutstandingRepaintRequest)
>-        return;
>-
>-    m_hasOutstandingRepaintRequest = true;
>-
>-    uint64_t pageID = m_webPageProxy.pageID();
>-    GestureID gestureID = m_currentGestureID;
>-    m_webPageProxy.forceRepaint(VoidCallback::create([pageID, gestureID] (CallbackBase::Error error) {
>-        if (auto gestureController = controllerForGesture(pageID, gestureID))
>-            gestureController->removeSwipeSnapshot();
>-    }));
>-}
>-
> void ViewGestureController::removeSwipeSnapshot()
> {
>     m_snapshotRemovalTracker.reset();
>@@ -844,17 +645,6 @@ bool ViewGestureController::completeSimulatedSwipeInDirectionForTesting(SwipeDir
>     return false;
> }
> 
>-void ViewGestureController::requestRenderTreeSizeNotificationIfNeeded()
>-{
>-    if (!m_snapshotRemovalTracker.hasOutstandingEvent(SnapshotRemovalTracker::RenderTreeSizeThreshold))
>-        return;
>-
>-    auto& process = m_webPageProxy.provisionalPageProxy() ? m_webPageProxy.provisionalPageProxy()->process() : m_webPageProxy.process();
>-    auto threshold = m_snapshotRemovalTracker.renderTreeSizeThreshold();
>-
>-    process.send(Messages::ViewGestureGeometryCollector::SetRenderTreeSizeNotificationThreshold(threshold), m_webPageProxy.pageID());
>-}
>-
> } // namespace WebKit
> 
> #endif // PLATFORM(MAC)
>diff --git a/Source/WebKit/UIProcess/mac/ViewSnapshotStore.h b/Source/WebKit/UIProcess/mac/ViewSnapshotStore.h
>deleted file mode 100644
>index b06f1f4dbb2976ce98d6f1bf61fd7f16aee1bb2e..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/mac/ViewSnapshotStore.h
>+++ /dev/null
>@@ -1,149 +0,0 @@
>-/*
>- * Copyright (C) 2014 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#ifndef ViewSnapshotStore_h
>-#define ViewSnapshotStore_h
>-
>-#include <WebCore/Color.h>
>-#include <WebCore/IntPoint.h>
>-#include <WebCore/IntSize.h>
>-#include <WebCore/IOSurface.h>
>-#include <wtf/ListHashSet.h>
>-#include <wtf/Noncopyable.h>
>-#include <wtf/RefCounted.h>
>-#include <wtf/text/WTFString.h>
>-
>-#if !defined(__OBJC__)
>-typedef struct objc_object *id;
>-#endif
>-
>-OBJC_CLASS CAContext;
>-
>-#if HAVE(IOSURFACE)
>-namespace WebCore {
>-class IOSurface;
>-}
>-#endif
>-
>-namespace WebKit {
>-
>-class ViewSnapshotStore;
>-class WebBackForwardListItem;
>-class WebPageProxy;
>-
>-class ViewSnapshot : public RefCounted<ViewSnapshot> {
>-public:
>-#if HAVE(IOSURFACE)
>-    static Ref<ViewSnapshot> create(std::unique_ptr<WebCore::IOSurface>);
>-#else
>-    static Ref<ViewSnapshot> create(uint32_t slotID, WebCore::IntSize, size_t imageSizeInBytes);
>-#endif
>-
>-    ~ViewSnapshot();
>-
>-    void clearImage();
>-    bool hasImage() const;
>-    id asLayerContents();
>-    RetainPtr<CGImageRef> asImageForTesting();
>-
>-    void setRenderTreeSize(uint64_t renderTreeSize) { m_renderTreeSize = renderTreeSize; }
>-    uint64_t renderTreeSize() const { return m_renderTreeSize; }
>-
>-    void setBackgroundColor(WebCore::Color color) { m_backgroundColor = color; }
>-    WebCore::Color backgroundColor() const { return m_backgroundColor; }
>-    
>-    void setViewScrollPosition(WebCore::IntPoint scrollPosition) { m_viewScrollPosition = scrollPosition; }
>-    WebCore::IntPoint viewScrollPosition() const { return m_viewScrollPosition; }
>-
>-    void setDeviceScaleFactor(float deviceScaleFactor) { m_deviceScaleFactor = deviceScaleFactor; }
>-    float deviceScaleFactor() const { return m_deviceScaleFactor; }
>-
>-#if HAVE(IOSURFACE)
>-    WebCore::IOSurface* surface() const { return m_surface.get(); }
>-
>-    size_t imageSizeInBytes() const { return m_surface ? m_surface->totalBytes() : 0; }
>-    WebCore::IntSize size() const { return m_surface ? m_surface->size() : WebCore::IntSize(); }
>-
>-    void setSurface(std::unique_ptr<WebCore::IOSurface>);
>-
>-    WebCore::IOSurface::SurfaceState setVolatile(bool);
>-#else
>-    WebCore::IntSize size() const { return m_size; }
>-    size_t imageSizeInBytes() const { return m_imageSizeInBytes; }
>-#endif
>-
>-private:
>-#if HAVE(IOSURFACE)
>-    explicit ViewSnapshot(std::unique_ptr<WebCore::IOSurface>);
>-
>-    std::unique_ptr<WebCore::IOSurface> m_surface;
>-#else
>-    explicit ViewSnapshot(uint32_t slotID, WebCore::IntSize, size_t imageSizeInBytes);
>-
>-    uint32_t m_slotID;
>-    size_t m_imageSizeInBytes;
>-    WebCore::IntSize m_size;
>-#endif
>-
>-    uint64_t m_renderTreeSize;
>-    float m_deviceScaleFactor;
>-    WebCore::Color m_backgroundColor;
>-    WebCore::IntPoint m_viewScrollPosition; // Scroll position at snapshot time. Integral to make comparison reliable.
>-};
>-
>-class ViewSnapshotStore {
>-    WTF_MAKE_NONCOPYABLE(ViewSnapshotStore);
>-    friend class ViewSnapshot;
>-public:
>-    ViewSnapshotStore();
>-    ~ViewSnapshotStore();
>-
>-    static ViewSnapshotStore& singleton();
>-
>-    void recordSnapshot(WebPageProxy&, WebBackForwardListItem&);
>-
>-    void discardSnapshotImages();
>-
>-    void setDisableSnapshotVolatilityForTesting(bool disable) { m_disableSnapshotVolatility = disable; }
>-    bool disableSnapshotVolatilityForTesting() const { return m_disableSnapshotVolatility; }
>-
>-#if !HAVE(IOSURFACE) && HAVE(CORE_ANIMATION_RENDER_SERVER)
>-    static CAContext *snapshottingContext();
>-#endif
>-
>-private:
>-    void didAddImageToSnapshot(ViewSnapshot&);
>-    void willRemoveImageFromSnapshot(ViewSnapshot&);
>-    void pruneSnapshots(WebPageProxy&);
>-
>-    size_t m_snapshotCacheSize { 0 };
>-
>-    ListHashSet<ViewSnapshot*> m_snapshotsWithImages;
>-    bool m_disableSnapshotVolatility { false };
>-};
>-
>-} // namespace WebKit
>-
>-#endif // ViewSnapshotStore_h
>diff --git a/Source/WebKit/UIProcess/mac/ViewSnapshotStore.mm b/Source/WebKit/UIProcess/mac/ViewSnapshotStore.mm
>deleted file mode 100644
>index 1fef6943e05c43e264c5cb5d2e7d2b7a59ca724c..0000000000000000000000000000000000000000
>--- a/Source/WebKit/UIProcess/mac/ViewSnapshotStore.mm
>+++ /dev/null
>@@ -1,249 +0,0 @@
>-/*
>- * Copyright (C) 2014 Apple Inc. All rights reserved.
>- *
>- * Redistribution and use in source and binary forms, with or without
>- * modification, are permitted provided that the following conditions
>- * are met:
>- * 1. Redistributions of source code must retain the above copyright
>- *    notice, this list of conditions and the following disclaimer.
>- * 2. Redistributions in binary form must reproduce the above copyright
>- *    notice, this list of conditions and the following disclaimer in the
>- *    documentation and/or other materials provided with the distribution.
>- *
>- * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>- * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>- * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>- * THE POSSIBILITY OF SUCH DAMAGE.
>- */
>-
>-#import "config.h"
>-#import "ViewSnapshotStore.h"
>-
>-#import "WebBackForwardList.h"
>-#import "WebPageProxy.h"
>-#import <CoreGraphics/CoreGraphics.h>
>-#import <WebCore/IOSurface.h>
>-
>-#if PLATFORM(IOS_FAMILY)
>-#import <pal/spi/cocoa/QuartzCoreSPI.h>
>-#endif
>-
>-#if PLATFORM(IOS_FAMILY)
>-static const size_t maximumSnapshotCacheSize = 50 * (1024 * 1024);
>-#else
>-static const size_t maximumSnapshotCacheSize = 400 * (1024 * 1024);
>-#endif
>-
>-namespace WebKit {
>-using namespace WebCore;
>-
>-ViewSnapshotStore::ViewSnapshotStore()
>-{
>-}
>-
>-ViewSnapshotStore::~ViewSnapshotStore()
>-{
>-    discardSnapshotImages();
>-}
>-
>-ViewSnapshotStore& ViewSnapshotStore::singleton()
>-{
>-    static ViewSnapshotStore& store = *new ViewSnapshotStore;
>-    return store;
>-}
>-
>-#if !HAVE(IOSURFACE) && HAVE(CORE_ANIMATION_RENDER_SERVER)
>-CAContext *ViewSnapshotStore::snapshottingContext()
>-{
>-    static CAContext *context;
>-    static dispatch_once_t onceToken;
>-    dispatch_once(&onceToken, ^{
>-        NSDictionary *options = @{
>-            kCAContextDisplayName: @"WebKitSnapshotting",
>-            kCAContextIgnoresHitTest: @YES,
>-            kCAContextDisplayId : @20000
>-        };
>-        context = [[CAContext remoteContextWithOptions:options] retain];
>-    });
>-
>-    return context;
>-}
>-#endif
>-
>-void ViewSnapshotStore::didAddImageToSnapshot(ViewSnapshot& snapshot)
>-{
>-    bool isNewEntry = m_snapshotsWithImages.add(&snapshot).isNewEntry;
>-    ASSERT_UNUSED(isNewEntry, isNewEntry);
>-    m_snapshotCacheSize += snapshot.imageSizeInBytes();
>-}
>-
>-void ViewSnapshotStore::willRemoveImageFromSnapshot(ViewSnapshot& snapshot)
>-{
>-    bool removed = m_snapshotsWithImages.remove(&snapshot);
>-    ASSERT_UNUSED(removed, removed);
>-    m_snapshotCacheSize -= snapshot.imageSizeInBytes();
>-}
>-
>-void ViewSnapshotStore::pruneSnapshots(WebPageProxy& webPageProxy)
>-{
>-    if (m_snapshotCacheSize <= maximumSnapshotCacheSize)
>-        return;
>-
>-    ASSERT(!m_snapshotsWithImages.isEmpty());
>-
>-    // FIXME: We have enough information to do smarter-than-LRU eviction (making use of the back-forward lists, etc.)
>-
>-    m_snapshotsWithImages.first()->clearImage();
>-}
>-
>-void ViewSnapshotStore::recordSnapshot(WebPageProxy& webPageProxy, WebBackForwardListItem& item)
>-{
>-    if (webPageProxy.isShowingNavigationGestureSnapshot())
>-        return;
>-
>-    pruneSnapshots(webPageProxy);
>-
>-    webPageProxy.willRecordNavigationSnapshot(item);
>-
>-    auto snapshot = webPageProxy.takeViewSnapshot();
>-    if (!snapshot)
>-        return;
>-
>-    snapshot->setRenderTreeSize(webPageProxy.renderTreeSize());
>-    snapshot->setDeviceScaleFactor(webPageProxy.deviceScaleFactor());
>-    snapshot->setBackgroundColor(webPageProxy.pageExtendedBackgroundColor());
>-    snapshot->setViewScrollPosition(WebCore::roundedIntPoint(webPageProxy.viewScrollPosition()));
>-
>-    item.setSnapshot(WTFMove(snapshot));
>-}
>-
>-void ViewSnapshotStore::discardSnapshotImages()
>-{
>-    while (!m_snapshotsWithImages.isEmpty())
>-        m_snapshotsWithImages.first()->clearImage();
>-}
>-
>-#if HAVE(IOSURFACE)
>-Ref<ViewSnapshot> ViewSnapshot::create(std::unique_ptr<WebCore::IOSurface> surface)
>-{
>-    return adoptRef(*new ViewSnapshot(WTFMove(surface)));
>-}
>-#else
>-Ref<ViewSnapshot> ViewSnapshot::create(uint32_t slotID, IntSize size, size_t imageSizeInBytes)
>-{
>-    return adoptRef(*new ViewSnapshot(slotID, size, imageSizeInBytes));
>-}
>-#endif
>-
>-#if HAVE(IOSURFACE)
>-ViewSnapshot::ViewSnapshot(std::unique_ptr<WebCore::IOSurface> surface)
>-    : m_surface(WTFMove(surface))
>-#else
>-ViewSnapshot::ViewSnapshot(uint32_t slotID, IntSize size, size_t imageSizeInBytes)
>-    : m_slotID(slotID)
>-    , m_imageSizeInBytes(imageSizeInBytes)
>-    , m_size(size)
>-#endif
>-{
>-    if (hasImage())
>-        ViewSnapshotStore::singleton().didAddImageToSnapshot(*this);
>-}
>-
>-ViewSnapshot::~ViewSnapshot()
>-{
>-    clearImage();
>-}
>-
>-#if HAVE(IOSURFACE)
>-void ViewSnapshot::setSurface(std::unique_ptr<WebCore::IOSurface> surface)
>-{
>-    ASSERT(!m_surface);
>-    if (!surface) {
>-        clearImage();
>-        return;
>-    }
>-
>-    m_surface = WTFMove(surface);
>-    ViewSnapshotStore::singleton().didAddImageToSnapshot(*this);
>-}
>-#endif
>-
>-bool ViewSnapshot::hasImage() const
>-{
>-#if HAVE(IOSURFACE)
>-    return !!m_surface;
>-#else
>-    return m_slotID;
>-#endif
>-}
>-
>-void ViewSnapshot::clearImage()
>-{
>-    if (!hasImage())
>-        return;
>-
>-    ViewSnapshotStore::singleton().willRemoveImageFromSnapshot(*this);
>-
>-#if HAVE(IOSURFACE)
>-    m_surface = nullptr;
>-#else
>-#if HAVE(CORE_ANIMATION_RENDER_SERVER)
>-    [ViewSnapshotStore::snapshottingContext() deleteSlot:m_slotID];
>-#endif
>-    m_slotID = 0;
>-    m_imageSizeInBytes = 0;
>-#endif
>-}
>-
>-#if HAVE(IOSURFACE)
>-WebCore::IOSurface::SurfaceState ViewSnapshot::setVolatile(bool becomeVolatile)
>-{
>-    if (ViewSnapshotStore::singleton().disableSnapshotVolatilityForTesting())
>-        return WebCore::IOSurface::SurfaceState::Valid;
>-
>-    if (!m_surface)
>-        return WebCore::IOSurface::SurfaceState::Empty;
>-
>-    return m_surface->setIsVolatile(becomeVolatile);
>-}
>-#endif
>-
>-id ViewSnapshot::asLayerContents()
>-{
>-#if HAVE(IOSURFACE)
>-    if (!m_surface)
>-        return nullptr;
>-
>-    if (setVolatile(false) != WebCore::IOSurface::SurfaceState::Valid) {
>-        clearImage();
>-        return nullptr;
>-    }
>-
>-    return m_surface->asLayerContents();
>-#else
>-    return [CAContext objectForSlot:m_slotID];
>-#endif
>-}
>-
>-RetainPtr<CGImageRef> ViewSnapshot::asImageForTesting()
>-{
>-#if HAVE(IOSURFACE)
>-    if (!m_surface)
>-        return nullptr;
>-
>-    ASSERT(ViewSnapshotStore::singleton().disableSnapshotVolatilityForTesting());
>-    return m_surface->createImage();
>-#else
>-    // FIXME: Implement this in the slot case.
>-    return nullptr;
>-#endif
>-}
>-
>-} // namespace WebKit
>diff --git a/Source/WebKit/UIProcess/mac/ViewSnapshotStoreMac.mm b/Source/WebKit/UIProcess/mac/ViewSnapshotStoreMac.mm
>new file mode 100644
>index 0000000000000000000000000000000000000000..35bc7c2eb990e8f41e87cc34d11c31f8b6d93d5e
>--- /dev/null
>+++ b/Source/WebKit/UIProcess/mac/ViewSnapshotStoreMac.mm
>@@ -0,0 +1,168 @@
>+/*
>+ * Copyright (C) 2014 Apple Inc. All rights reserved.
>+ *
>+ * Redistribution and use in source and binary forms, with or without
>+ * modification, are permitted provided that the following conditions
>+ * are met:
>+ * 1. Redistributions of source code must retain the above copyright
>+ *    notice, this list of conditions and the following disclaimer.
>+ * 2. Redistributions in binary form must reproduce the above copyright
>+ *    notice, this list of conditions and the following disclaimer in the
>+ *    documentation and/or other materials provided with the distribution.
>+ *
>+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
>+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
>+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
>+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
>+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
>+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
>+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
>+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
>+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
>+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
>+ * THE POSSIBILITY OF SUCH DAMAGE.
>+ */
>+
>+#import "config.h"
>+#import "ViewSnapshotStore.h"
>+
>+#import <CoreGraphics/CoreGraphics.h>
>+#import <WebCore/IOSurface.h>
>+
>+#if PLATFORM(IOS_FAMILY)
>+#import <pal/spi/cocoa/QuartzCoreSPI.h>
>+#endif
>+
>+namespace WebKit {
>+using namespace WebCore;
>+
>+#if !HAVE(IOSURFACE) && HAVE(CORE_ANIMATION_RENDER_SERVER)
>+CAContext *ViewSnapshotStore::snapshottingContext()
>+{
>+    static CAContext *context;
>+    static dispatch_once_t onceToken;
>+    dispatch_once(&onceToken, ^{
>+        NSDictionary *options = @{
>+            kCAContextDisplayName: @"WebKitSnapshotting",
>+            kCAContextIgnoresHitTest: @YES,
>+            kCAContextDisplayId : @20000
>+        };
>+        context = [[CAContext remoteContextWithOptions:options] retain];
>+    });
>+
>+    return context;
>+}
>+#endif
>+
>+#if HAVE(IOSURFACE)
>+Ref<ViewSnapshot> ViewSnapshot::create(std::unique_ptr<WebCore::IOSurface> surface)
>+{
>+    return adoptRef(*new ViewSnapshot(WTFMove(surface)));
>+}
>+#else
>+Ref<ViewSnapshot> ViewSnapshot::create(uint32_t slotID, IntSize size, size_t imageSizeInBytes)
>+{
>+    return adoptRef(*new ViewSnapshot(slotID, size, imageSizeInBytes));
>+}
>+#endif
>+
>+#if HAVE(IOSURFACE)
>+ViewSnapshot::ViewSnapshot(std::unique_ptr<WebCore::IOSurface> surface)
>+    : m_surface(WTFMove(surface))
>+#else
>+ViewSnapshot::ViewSnapshot(uint32_t slotID, IntSize size, size_t imageSizeInBytes)
>+    : m_slotID(slotID)
>+    , m_imageSizeInBytes(imageSizeInBytes)
>+    , m_size(size)
>+#endif
>+{
>+    if (hasImage())
>+        ViewSnapshotStore::singleton().didAddImageToSnapshot(*this);
>+}
>+
>+#if HAVE(IOSURFACE)
>+void ViewSnapshot::setSurface(std::unique_ptr<WebCore::IOSurface> surface)
>+{
>+    ASSERT(!m_surface);
>+    if (!surface) {
>+        clearImage();
>+        return;
>+    }
>+
>+    m_surface = WTFMove(surface);
>+    ViewSnapshotStore::singleton().didAddImageToSnapshot(*this);
>+}
>+#endif
>+
>+bool ViewSnapshot::hasImage() const
>+{
>+#if HAVE(IOSURFACE)
>+    return !!m_surface;
>+#else
>+    return m_slotID;
>+#endif
>+}
>+
>+void ViewSnapshot::clearImage()
>+{
>+    if (!hasImage())
>+        return;
>+
>+    ViewSnapshotStore::singleton().willRemoveImageFromSnapshot(*this);
>+
>+#if HAVE(IOSURFACE)
>+    m_surface = nullptr;
>+#else
>+#if HAVE(CORE_ANIMATION_RENDER_SERVER)
>+    [ViewSnapshotStore::snapshottingContext() deleteSlot:m_slotID];
>+#endif
>+    m_slotID = 0;
>+    m_imageSizeInBytes = 0;
>+#endif
>+}
>+
>+#if HAVE(IOSURFACE)
>+WebCore::IOSurface::SurfaceState ViewSnapshot::setVolatile(bool becomeVolatile)
>+{
>+    if (ViewSnapshotStore::singleton().disableSnapshotVolatilityForTesting())
>+        return WebCore::IOSurface::SurfaceState::Valid;
>+
>+    if (!m_surface)
>+        return WebCore::IOSurface::SurfaceState::Empty;
>+
>+    return m_surface->setIsVolatile(becomeVolatile);
>+}
>+#endif
>+
>+id ViewSnapshot::asLayerContents()
>+{
>+#if HAVE(IOSURFACE)
>+    if (!m_surface)
>+        return nullptr;
>+
>+    if (setVolatile(false) != WebCore::IOSurface::SurfaceState::Valid) {
>+        clearImage();
>+        return nullptr;
>+    }
>+
>+    return m_surface->asLayerContents();
>+#else
>+    return [CAContext objectForSlot:m_slotID];
>+#endif
>+}
>+
>+RetainPtr<CGImageRef> ViewSnapshot::asImageForTesting()
>+{
>+#if HAVE(IOSURFACE)
>+    if (!m_surface)
>+        return nullptr;
>+
>+    ASSERT(ViewSnapshotStore::singleton().disableSnapshotVolatilityForTesting());
>+    return m_surface->createImage();
>+#else
>+    // FIXME: Implement this in the slot case.
>+    return nullptr;
>+#endif
>+}
>+
>+} // namespace WebKit
>diff --git a/Source/WebKit/WebKit.xcodeproj/project.pbxproj b/Source/WebKit/WebKit.xcodeproj/project.pbxproj
>index 3eacefc54b1bf154185874bc28a6f4743e2609bd..9b253418fadb387793900013348f678556ea6e9e 100644
>--- a/Source/WebKit/WebKit.xcodeproj/project.pbxproj
>+++ b/Source/WebKit/WebKit.xcodeproj/project.pbxproj
>@@ -586,7 +586,7 @@
> 		2D3A65DF1A7C3A7D00CAC637 /* WKNavigationResponseRef.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D3A65DD1A7C3A7D00CAC637 /* WKNavigationResponseRef.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		2D3A65E31A7C3A9300CAC637 /* WKNavigationRef.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D3A65E11A7C3A9300CAC637 /* WKNavigationRef.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		2D3A65E71A7C3AA700CAC637 /* WKFrameInfoRef.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D3A65E51A7C3AA700CAC637 /* WKFrameInfoRef.h */; settings = {ATTRIBUTES = (Private, ); }; };
>-		2D3EF4431917646300034184 /* WebMemoryPressureHandlerCocoa.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D3EF4411917646300034184 /* WebMemoryPressureHandlerCocoa.h */; };
>+		2D3EF4431917646300034184 /* WebMemoryPressureHandler.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D3EF4411917646300034184 /* WebMemoryPressureHandler.h */; };
> 		2D47B56D1810714E003A3AEE /* RemoteLayerBackingStore.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D47B56B1810714E003A3AEE /* RemoteLayerBackingStore.h */; };
> 		2D4AF0892044C3C4006C8817 /* FrontBoardServicesSPI.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D4AF0882044C3C4006C8817 /* FrontBoardServicesSPI.h */; };
> 		2D4D2C811DF60BF3002EB10C /* InteractionInformationRequest.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D4D2C7F1DF60BF3002EB10C /* InteractionInformationRequest.h */; };
>@@ -618,6 +618,7 @@
> 		2D6AB541192B1C4A003A9FD1 /* WKPDFPageNumberIndicator.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D6AB53F192B1C4A003A9FD1 /* WKPDFPageNumberIndicator.h */; };
> 		2D6B371B18A967AD0042AE80 /* _WKThumbnailView.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D6B371918A967AD0042AE80 /* _WKThumbnailView.h */; settings = {ATTRIBUTES = (Private, ); }; };
> 		2D6BF12421AF56E1001E79C9 /* PencilKitSoftLink.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D6BF12221AF56E1001E79C9 /* PencilKitSoftLink.h */; };
>+		2D6CD11B189058A500E5A4A0 /* ViewSnapshotStore.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 2D6CD11A189058A500E5A4A0 /* ViewSnapshotStore.cpp */; };
> 		2D6CD119189058A500E5A4A0 /* ViewSnapshotStore.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D6CD117189058A500E5A4A0 /* ViewSnapshotStore.h */; };
> 		2D72A1FA212BF46E00517A20 /* RemoteLayerTreeDrawingArea.mm in Sources */ = {isa = PBXBuildFile; fileRef = 1AB16ADB1648598400290D62 /* RemoteLayerTreeDrawingArea.mm */; };
> 		2D7303791A7C2B7500F8F487 /* WKPageNavigationClient.h in Headers */ = {isa = PBXBuildFile; fileRef = 2D7303781A7C2B7500F8F487 /* WKPageNavigationClient.h */; settings = {ATTRIBUTES = (Private, ); }; };
>@@ -2468,6 +2469,7 @@
> 		2D1087621D2C641B00B85F82 /* LoadParametersCocoa.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = LoadParametersCocoa.mm; sourceTree = "<group>"; };
> 		2D125C5C1857EA05003BA3CB /* ViewGestureController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ViewGestureController.h; sourceTree = "<group>"; };
> 		2D125C5D1857EA05003BA3CB /* ViewGestureControllerMac.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ViewGestureControllerMac.mm; sourceTree = "<group>"; };
>+		2D6CD118189058A500E5A4A0 /* ViewSnapshotStoreMac.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ViewSnapshotStoreMac.mm; sourceTree = "<group>"; };
> 		2D12DAB420662C73006F00FB /* WKAnimationDelegate.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WKAnimationDelegate.h; sourceTree = "<group>"; };
> 		2D1B5D5A18586599006C6596 /* ViewGestureController.messages.in */ = {isa = PBXFileReference; lastKnownFileType = text; path = ViewGestureController.messages.in; sourceTree = "<group>"; };
> 		2D1B5D5B185869C8006C6596 /* ViewGestureControllerMessageReceiver.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = ViewGestureControllerMessageReceiver.cpp; path = DerivedSources/WebKit2/ViewGestureControllerMessageReceiver.cpp; sourceTree = BUILT_PRODUCTS_DIR; };
>@@ -2498,8 +2500,8 @@
> 		2D3A65E11A7C3A9300CAC637 /* WKNavigationRef.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WKNavigationRef.h; sourceTree = "<group>"; };
> 		2D3A65E41A7C3AA700CAC637 /* WKFrameInfoRef.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = WKFrameInfoRef.cpp; sourceTree = "<group>"; };
> 		2D3A65E51A7C3AA700CAC637 /* WKFrameInfoRef.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WKFrameInfoRef.h; sourceTree = "<group>"; };
>-		2D3EF4401917646300034184 /* WebMemoryPressureHandlerCocoa.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = WebMemoryPressureHandlerCocoa.mm; sourceTree = "<group>"; };
>-		2D3EF4411917646300034184 /* WebMemoryPressureHandlerCocoa.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WebMemoryPressureHandlerCocoa.h; sourceTree = "<group>"; };
>+		2D3EF4401917646300034184 /* WebMemoryPressureHandler.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = WebMemoryPressureHandler.cpp; sourceTree = "<group>"; };
>+		2D3EF4411917646300034184 /* WebMemoryPressureHandler.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WebMemoryPressureHandler.h; sourceTree = "<group>"; };
> 		2D429BFA1721E2BA00EC681F /* PDFPluginPasswordField.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = PDFPluginPasswordField.h; path = PDF/PDFPluginPasswordField.h; sourceTree = "<group>"; };
> 		2D429BFB1721E2BA00EC681F /* PDFPluginPasswordField.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; name = PDFPluginPasswordField.mm; path = PDF/PDFPluginPasswordField.mm; sourceTree = "<group>"; };
> 		2D47B56A1810714E003A3AEE /* RemoteLayerBackingStore.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = RemoteLayerBackingStore.mm; sourceTree = "<group>"; };
>@@ -2543,7 +2545,7 @@
> 		2D6BF12121AF56E1001E79C9 /* PencilKitSoftLink.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; name = PencilKitSoftLink.mm; path = ios/PencilKitSoftLink.mm; sourceTree = "<group>"; };
> 		2D6BF12221AF56E1001E79C9 /* PencilKitSoftLink.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = PencilKitSoftLink.h; path = ios/PencilKitSoftLink.h; sourceTree = "<group>"; };
> 		2D6CD117189058A500E5A4A0 /* ViewSnapshotStore.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ViewSnapshotStore.h; sourceTree = "<group>"; };
>-		2D6CD118189058A500E5A4A0 /* ViewSnapshotStore.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ViewSnapshotStore.mm; sourceTree = "<group>"; };
>+		2D6CD11A189058A500E5A4A0 /* ViewSnapshotStore.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = ViewSnapshotStore.cpp; sourceTree = "<group>"; };
> 		2D7303781A7C2B7500F8F487 /* WKPageNavigationClient.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WKPageNavigationClient.h; sourceTree = "<group>"; };
> 		2D790A9C1AD7050D00AB90B3 /* _WKLayoutMode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = _WKLayoutMode.h; sourceTree = "<group>"; };
> 		2D790A9E1AD7164900AB90B3 /* WKLayoutMode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = WKLayoutMode.h; sourceTree = "<group>"; };
>@@ -5329,11 +5331,6 @@
> 				52D5A1AA1C57494E00DE34A3 /* VideoFullscreenManagerProxy.h */,
> 				52D5A1AB1C57494E00DE34A3 /* VideoFullscreenManagerProxy.messages.in */,
> 				52D5A1AC1C57494E00DE34A3 /* VideoFullscreenManagerProxy.mm */,
>-				2DAF4FFA1B636181006013D6 /* ViewGestureController.cpp */,
>-				2D125C5C1857EA05003BA3CB /* ViewGestureController.h */,
>-				2D1B5D5A18586599006C6596 /* ViewGestureController.messages.in */,
>-				2D3EF4411917646300034184 /* WebMemoryPressureHandlerCocoa.h */,
>-				2D3EF4401917646300034184 /* WebMemoryPressureHandlerCocoa.mm */,
> 				1AC0273E196622D600C12B75 /* WebPageProxyCocoa.mm */,
> 				7C4694CB1A4B510A00AD5845 /* WebPasteboardProxyCocoa.mm */,
> 				7CE4D2151A49148400C7F152 /* WebProcessPoolCocoa.mm */,
>@@ -7407,6 +7404,11 @@
> 				4A410F3C19AF7B04002EBAB5 /* UserMediaPermissionRequestProxy.h */,
> 				074E75FC1DF2002400D318EC /* UserMediaProcessManager.cpp */,
> 				074E75FB1DF1FD1300D318EC /* UserMediaProcessManager.h */,
>+				2DAF4FFA1B636181006013D6 /* ViewGestureController.cpp */,
>+				2D125C5C1857EA05003BA3CB /* ViewGestureController.h */,
>+				2D1B5D5A18586599006C6596 /* ViewGestureController.messages.in */,
>+				2D6CD11A189058A500E5A4A0 /* ViewSnapshotStore.cpp */,
>+				2D6CD117189058A500E5A4A0 /* ViewSnapshotStore.h */,
> 				2DD5A7281EBF08D5009BA597 /* VisibleWebPageCounter.h */,
> 				1A0F29E1120B44420053D1B9 /* VisitedLinkStore.cpp */,
> 				1A0F29E2120B44420053D1B9 /* VisitedLinkStore.h */,
>@@ -7463,6 +7465,8 @@
> 				C98C48A41B6FD4C300145103 /* WebMediaSessionFocusManager.h */,
> 				C9C183371B73FD6A007036A7 /* WebMediaSessionFocusManagerClient.cpp */,
> 				C9C183381B73FD6A007036A7 /* WebMediaSessionFocusManagerClient.h */,
>+				2D3EF4411917646300034184 /* WebMemoryPressureHandler.h */,
>+				2D3EF4401917646300034184 /* WebMemoryPressureHandler.mm */,
> 				7CCCC8F81A5F50FD008FB0DA /* WebNavigationState.cpp */,
> 				7CCCC8F91A5F50FD008FB0DA /* WebNavigationState.h */,
> 				BC1DFEA312B31F87005DF730 /* WebOpenPanelResultListenerProxy.cpp */,
>@@ -8207,8 +8211,7 @@
> 				CD491B111E73482100009066 /* UserMediaCaptureManagerProxy.h */,
> 				CD491B141E7349F300009066 /* UserMediaCaptureManagerProxy.messages.in */,
> 				2D125C5D1857EA05003BA3CB /* ViewGestureControllerMac.mm */,
>-				2D6CD117189058A500E5A4A0 /* ViewSnapshotStore.h */,
>-				2D6CD118189058A500E5A4A0 /* ViewSnapshotStore.mm */,
>+				2D6CD118189058A500E5A4A0 /* ViewSnapshotStoreMac.mm */,
> 				728E86EF1795188C0087879E /* WebColorPickerMac.h */,
> 				728E86F01795188C0087879E /* WebColorPickerMac.mm */,
> 				51ACBB9E127A8F2C00D203B9 /* WebContextMenuProxyMac.h */,
>@@ -9496,7 +9499,7 @@
> 				C98C48A61B6FD4C300145103 /* WebMediaSessionFocusManager.h in Headers */,
> 				C9C1833C1B74026D007036A7 /* WebMediaSessionFocusManagerClient.h in Headers */,
> 				C9CD43981B4B001D00239E33 /* WebMediaSessionMetadata.h in Headers */,
>-				2D3EF4431917646300034184 /* WebMemoryPressureHandlerCocoa.h in Headers */,
>+				2D3EF4431917646300034184 /* WebMemoryPressureHandler.h in Headers */,
> 				909854ED12BC4E18000AD080 /* WebMemorySampler.h in Headers */,
> 				513FFB91201459C6002596EA /* WebMessagePortChannelProvider.h in Headers */,
> 				BCF69F9A1176CED600471A52 /* WebNavigationDataStore.h in Headers */,
>@@ -11028,6 +11031,7 @@
> 				3F418EFB1887BD97002795FD /* VideoFullscreenManagerProxyMessageReceiver.cpp in Sources */,
> 				2D1B5D5D185869C8006C6596 /* ViewGestureControllerMessageReceiver.cpp in Sources */,
> 				2D819BA11862800E001F03D1 /* ViewGestureGeometryCollectorMessageReceiver.cpp in Sources */,
>+				2D6CD11B189058A500E5A4A0 /* ViewShapshotStore.cpp in Sources */,
> 				2684055218B86ED60022C38B /* ViewUpdateDispatcherMessageReceiver.cpp in Sources */,
> 				1A60224C18C16B9F00C3E8C9 /* VisitedLinkStoreMessageReceiver.cpp in Sources */,
> 				1A8E7D3C18C15149005A702A /* VisitedLinkTableControllerMessageReceiver.cpp in Sources */,
>diff --git a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.cpp b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.cpp
>index cf1968ee411e1d966b4377260081f8075ebdf2c6..9ea7eb49891d7120ec2e1ae1689e26e3bf46c2a6 100644
>--- a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.cpp
>+++ b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.cpp
>@@ -44,9 +44,7 @@
> 
> #if PLATFORM(IOS_FAMILY)
> #include "SmartMagnificationControllerMessages.h"
>-#endif
>-
>-#if PLATFORM(MAC)
>+#else
> #include "ViewGestureControllerMessages.h"
> #endif
> 
>@@ -59,7 +57,7 @@ static const double minimumScaleDifferenceForZooming = 0.3;
> 
> ViewGestureGeometryCollector::ViewGestureGeometryCollector(WebPage& webPage)
>     : m_webPage(webPage)
>-#if PLATFORM(MAC)
>+#if !PLATFORM(IOS_FAMILY)
>     , m_renderTreeSizeNotificationThreshold(0)
> #endif
> {
>@@ -237,12 +235,12 @@ void ViewGestureGeometryCollector::computeZoomInformationForNode(Node& node, Flo
> 
> void ViewGestureGeometryCollector::computeMinimumAndMaximumViewportScales(double& viewportMinimumScale, double& viewportMaximumScale) const
> {
>-#if PLATFORM(MAC)
>-    viewportMinimumScale = 0;
>-    viewportMaximumScale = std::numeric_limits<double>::max();
>-#else
>+#if PLATFORM(IOS_FAMILY)
>     viewportMinimumScale = m_webPage.minimumPageScaleFactor();
>     viewportMaximumScale = m_webPage.maximumPageScaleFactor();
>+#else
>+    viewportMinimumScale = 0;
>+    viewportMaximumScale = std::numeric_limits<double>::max();
> #endif
> }
> 
>@@ -253,7 +251,9 @@ void ViewGestureGeometryCollector::collectGeometryForMagnificationGesture()
>     bool frameHandlesMagnificationGesture = m_webPage.mainWebFrame()->handlesPageScaleGesture();
>     m_webPage.send(Messages::ViewGestureController::DidCollectGeometryForMagnificationGesture(visibleContentRect, frameHandlesMagnificationGesture));
> }
>+#endif
> 
>+#if !PLATFORM(IOS_FAMILY)
> void ViewGestureGeometryCollector::setRenderTreeSizeNotificationThreshold(uint64_t size)
> {
>     m_renderTreeSizeNotificationThreshold = size;
>@@ -273,8 +273,7 @@ void ViewGestureGeometryCollector::mainFrameDidLayout()
> {
> #if PLATFORM(IOS_FAMILY)
>     m_cachedTextLegibilityScales.reset();
>-#endif
>-#if PLATFORM(MAC)
>+#else
>     sendDidHitRenderTreeSizeThresholdIfNeeded();
> #endif
> }
>diff --git a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.h b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.h
>index 2ac498d0e48851a033b9f30365ab02898d146bca..dc2b1fc4187b7d0a74821748479ec651d1ef9871 100644
>--- a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.h
>+++ b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.h
>@@ -55,6 +55,8 @@ private:
> 
> #if PLATFORM(MAC)
>     void collectGeometryForMagnificationGesture();
>+#endif
>+#if !PLATFORM(IOS_FAMILY)
>     void setRenderTreeSizeNotificationThreshold(uint64_t);
>     void sendDidHitRenderTreeSizeThresholdIfNeeded();
> #endif
>@@ -69,10 +71,9 @@ private:
> 
>     WebPage& m_webPage;
> 
>-#if PLATFORM(MAC)
>+#if !PLATFORM(IOS_FAMILY)
>     uint64_t m_renderTreeSizeNotificationThreshold;
>-#endif
>-#if PLATFORM(IOS_FAMILY)
>+#else
>     Optional<std::pair<double, double>> m_cachedTextLegibilityScales;
> #endif
> };
>diff --git a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.messages.in b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.messages.in
>index ad277614706f6ecd6d471eed32d6e177b539a448..5a002fb542375955886af0567562340f6b46b4e9 100644
>--- a/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.messages.in
>+++ b/Source/WebKit/WebProcess/WebPage/ViewGestureGeometryCollector.messages.in
>@@ -21,11 +21,15 @@
> # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> 
> messages -> ViewGestureGeometryCollector {
>+#if PLATFORM(COCOA)
>     CollectGeometryForSmartMagnificationGesture(WebCore::FloatPoint origin)
>+#endif
> 
>-#if !PLATFORM(IOS_FAMILY)
>+#if PLATFORM(MAC)
>     CollectGeometryForMagnificationGesture()
>+#endif
> 
>+#if !PLATFORM(IOS_FAMILY)
>     SetRenderTreeSizeNotificationThreshold(uint64_t size)
> #endif
> }
>diff --git a/Source/WebKit/WebProcess/WebPage/WebPage.cpp b/Source/WebKit/WebProcess/WebPage/WebPage.cpp
>index de34617e40fc26758000fc4ec9b590d2c9acf449..2023fe418d03152c8e0a80f6df9c98b808a23464 100644
>--- a/Source/WebKit/WebProcess/WebPage/WebPage.cpp
>+++ b/Source/WebKit/WebProcess/WebPage/WebPage.cpp
>@@ -363,7 +363,7 @@ WebPage::WebPage(uint64_t pageID, WebPageCreationParameters&& parameters)
>     , m_determinePrimarySnapshottedPlugInTimer(RunLoop::main(), this, &WebPage::determinePrimarySnapshottedPlugInTimerFired)
> #endif
>     , m_layerHostingMode(parameters.layerHostingMode)
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     , m_viewGestureGeometryCollector(makeUniqueRef<ViewGestureGeometryCollector>(*this))
> #elif HAVE(ACCESSIBILITY) && PLATFORM(GTK)
>     , m_accessibilityObject(nullptr)
>@@ -4218,7 +4218,7 @@ void WebPage::mainFrameDidLayout()
>         m_cachedPageCount = pageCount;
>     }
> 
>-#if PLATFORM(COCOA)
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     m_viewGestureGeometryCollector->mainFrameDidLayout();
> #endif
> #if PLATFORM(IOS_FAMILY)
>diff --git a/Source/WebKit/WebProcess/WebPage/WebPage.h b/Source/WebKit/WebProcess/WebPage/WebPage.h
>index 6062ad88bc9c13cc1fcc60bd7225452bafd5e222..e2460cbd27db384521d70e42bb4dab0619121aa0 100644
>--- a/Source/WebKit/WebProcess/WebPage/WebPage.h
>+++ b/Source/WebKit/WebProcess/WebPage/WebPage.h
>@@ -1579,9 +1579,13 @@ private:
>     WebCore::FloatPoint m_accessibilityPosition;
>     
>     RetainPtr<WKAccessibilityWebPageObject> m_mockAccessibilityElement;
>+#endif
> 
>+#if PLATFORM(COCOA) || PLATFORM(GTK)
>     UniqueRef<ViewGestureGeometryCollector> m_viewGestureGeometryCollector;
>+#endif
> 
>+#if PLATFORM(COCOA)
>     RetainPtr<NSDictionary> m_dataDetectionContext;
> #endif
> 
>diff --git a/Tools/ChangeLog b/Tools/ChangeLog
>index 7afbe313dadaf62d9b152e75785ed213cb999bf3..ead23336e212e38c4b0f0ad0de73cbee9da5e267 100644
>--- a/Tools/ChangeLog
>+++ b/Tools/ChangeLog
>@@ -1,3 +1,13 @@
>+2019-02-08  Alexander Mikhaylenko  <exalm7659@gmail.com>
>+
>+        [GTK] Implement back/forward touchpad gesture
>+        https://bugs.webkit.org/show_bug.cgi?id=193919
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * TestWebKitAPI/Tests/WebKitGLib/TestWebKitSettings.cpp:
>+        (testWebKitSettings): Add a test for 'enable-back-forward-navigation-gestures' property.
>+
> 2019-02-08  Benjamin Poulain  <benjamin@webkit.org>
> 
>         clampTo(): do not convert the input to double when dealing with integers
>diff --git a/Tools/TestWebKitAPI/Tests/WebKitGLib/TestWebKitSettings.cpp b/Tools/TestWebKitAPI/Tests/WebKitGLib/TestWebKitSettings.cpp
>index 3edd53ced97d32e9934adaa56bd612943788e49f..157f0a6436616a4ccf09b19fdd43acd5733a60b9 100644
>--- a/Tools/TestWebKitAPI/Tests/WebKitGLib/TestWebKitSettings.cpp
>+++ b/Tools/TestWebKitAPI/Tests/WebKitGLib/TestWebKitSettings.cpp
>@@ -348,6 +348,11 @@ static void testWebKitSettings(Test*, gconstpointer)
>     g_assert_cmpuint(webkit_settings_get_hardware_acceleration_policy(settings), ==, WEBKIT_HARDWARE_ACCELERATION_POLICY_ALWAYS);
>     webkit_settings_set_hardware_acceleration_policy(settings, WEBKIT_HARDWARE_ACCELERATION_POLICY_ON_DEMAND);
>     g_assert_cmpuint(webkit_settings_get_hardware_acceleration_policy(settings), ==, WEBKIT_HARDWARE_ACCELERATION_POLICY_ON_DEMAND);
>+
>+    // Back-forward navigation gesture is disabled by default
>+    g_assert_false(webkit_settings_get_enable_back_forward_navigation_gestures(settings));
>+    webkit_settings_set_enable_back_forward_navigation_gestures(settings, TRUE);
>+    g_assert_true(webkit_settings_get_enable_back_forward_navigation_gestures(settings));
> #endif
> 
>     g_object_unref(G_OBJECT(settings));

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