Attachment 360291 Details for Bug 157743 – WIP-004

[patch] WIP-004

ro-004.diff (text/plain), 80.91 KB, created by cathiechen on 2019-01-27 04:13:28 PST

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Creator: cathiechen

Created: 2019-01-27 04:13:28 PST

Size: 80.91 KB

patch

obsolete

>diff --git a/LayoutTests/imported/w3c/resources/import-expectations.json b/LayoutTests/imported/w3c/resources/import-expectations.json
>index d6ee94121c..3a0def66b0 100644
>--- a/LayoutTests/imported/w3c/resources/import-expectations.json
>+++ b/LayoutTests/imported/w3c/resources/import-expectations.json
>@@ -296,6 +296,7 @@
>     "web-platform-tests/remote-playback": "skip", 
>     "web-platform-tests/requestidlecallback": "skip", 
>     "web-platform-tests/resize-observer": "skip", 
>+    "web-platform-tests/resize-observer/": "import", 
>     "web-platform-tests/resource-timing": "import", 
>     "web-platform-tests/resources": "import", 
>     "web-platform-tests/screen-orientation": "skip", 
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/META.yml b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/META.yml
>new file mode 100644
>index 0000000000..ef6685622b
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/META.yml
>@@ -0,0 +1,4 @@
>+spec: https://wicg.github.io/ResizeObserver/
>+suggested_reviewers:
>+  - atotic
>+  - dholbert
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop-expected.txt
>new file mode 100644
>index 0000000000..e39d53828a
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop-expected.txt
>@@ -0,0 +1,10 @@
>+ResizeObserver notification event loop tests
>+
>+t1
>+
>+Harness Error (TIMEOUT), message = null
>+
>+PASS ResizeObserver implemented 
>+NOTRUN guard 
>+FAIL test0: multiple notifications inside same event loop assert_unreached: Timed out waiting for notification. (100ms) Reached unreachable code
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop.html
>new file mode 100644
>index 0000000000..622d724a19
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop.html
>@@ -0,0 +1,259 @@
>+<!doctype html>
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="./resources/resizeTestHelper.js"></script>
>+<style>
>+  div {
>+    border: 1px dotted gray
>+  }
>+</style>
>+<p>ResizeObserver notification event loop tests</p>
>+<div id="target1" style="width:100px;height:100px;">t1
>+</div>
>+<div id="container">
>+  <div id="a1" style="width:100px;height:100px">
>+    <div id="a2" style="width:100px;height:100px">
>+    </div>
>+  </div>
>+  <div id="b1" style="width:100px;height:100px">
>+    <div id="b2" style="width:100px;height:100px">
>+    </div>
>+  </div>
>+</div>
>+<script>
>+'use strict';
>+
>+let t1 = document.querySelector('#target1');
>+
>+// allow uncaught exception because ResizeObserver posts exceptions
>+// to window error handler when limit is exceeded.
>+// This codepath is tested in this file.
>+
>+setup({allow_uncaught_exception: true});
>+
>+function template() {
>+  let helper = new ResizeTestHelper(
>+    "test0: title",
>+  [
>+    {
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+var onErrorCalled = false;
>+
>+window.onerror = err => {
>+  onErrorCalled = true;
>+}
>+
>+function test0() {
>+
>+  let divs = [t1];
>+  let rAF = 0;
>+  let helper = new ResizeTestHelper(
>+    "test0: multiple notifications inside same event loop",
>+  [
>+    {
>+      setup: observer => {
>+        onErrorCalled = false;
>+        let t2 = document.createElement('div');
>+        let t3 = document.createElement('div');
>+        t2.appendChild(t3);
>+        t1.appendChild(t2);
>+        divs.push(t2);
>+        divs.push(t3);
>+        observer.observe(t1);
>+        observer.observe(t2);
>+        observer.observe(t3);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 3, "3 notifications");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        helper.startCountingRaf();
>+        divs.forEach( el => { el.style.width = "101px";});
>+      },
>+      notify: (entries, observer) => {
>+        // t1 is not delivered
>+        assert_equals(entries.length, 2, "2 notifications");
>+        assert_equals(helper.rafCount, 0, "still in same loop");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        divs.forEach( el => { el.style.width = "102px";});
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "1 notifications");
>+        assert_equals(helper.rafCount, 0, "same loop");
>+      }
>+    },
>+    { // t1 and t2 get notified
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 2, "2 notifications");
>+        assert_equals(helper.rafCount, 1, "new loop");
>+        assert_equals(onErrorCalled, true, "error was fired");
>+        observer.disconnect();
>+        while (t1.childNodes.length > 0)
>+          t1.removeChild(t1.childNodes[0]);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test1() {
>+
>+  var resizers = [t1];
>+  // Testing depths of shadow roots
>+  // DOM: t1 <- t2 <- t3 <-shadow- t4 <- t5
>+  let helper = new ResizeTestHelper(
>+    "test1: depths of shadow roots",
>+  [
>+    {
>+      setup: observer => {
>+        onErrorCalled = false;
>+        let t2 = document.createElement('div');
>+        t1.appendChild(t2);
>+        resizers.push(t2);
>+        let t3 = document.createElement('div');
>+        resizers.push(t3);
>+        t2.appendChild(t3);
>+        let shadow = t3.attachShadow({ mode: "open" });
>+        let t4 = document.createElement('div');
>+        resizers.push(t4);
>+        shadow.appendChild(t4);
>+        let t5 = document.createElement('div');
>+        resizers.push(t5);
>+        t4.appendChild(t5);
>+        resizers.forEach( el => observer.observe(el) );
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 5, "all entries resized");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        resizers.forEach( el => el.style.width = "111px" );
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 4, "depth limited");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        resizers.forEach( el => el.style.width = "112px" );
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 3, "depth limited");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        resizers.forEach( el => el.style.width = "113px" );
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 2, "depth limited");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        resizers.forEach( el => el.style.width = "114px" );
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "depth limited");
>+      }
>+    },
>+    {
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 4, "limit notifications");
>+        assert_equals(onErrorCalled, true, "breached limit");
>+        observer.disconnect();
>+        t1.removeChild(t1.firstChild);
>+      }
>+    },
>+  ]);
>+  return helper.start();
>+}
>+
>+function test2() {
>+  let container = document.querySelector('#container');
>+  let a1 = document.querySelector('#a1');
>+  let a2 = document.querySelector('#a2');
>+  let b1 = document.querySelector('#b1');
>+  let b2 = document.querySelector('#b2');
>+  let targets = [a1, a2, b1, b2];
>+
>+  let helper = new ResizeTestHelper(
>+    "test2: move target in dom while inside event loop",
>+  [
>+    {
>+      setup: observer => {
>+        for (let t of targets)
>+          observer.observe(t);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // delay next observation
>+      }
>+    },
>+    { // resize them all
>+      setup: observer => {
>+        for (let t of targets)
>+          t.style.width = "110px";
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, targets.length, "all targets observed");
>+      }
>+    },
>+    { // resize all, move dom upwards
>+      setup: observer => {
>+        for (let t of targets)
>+          t.style.width = "130px";
>+        container.appendChild(b2);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "b2 moved upwards");
>+        assert_equals(entries[0].target, a2);
>+      }
>+    },
>+    { // resize all, move dom downwards
>+      setup: observer => {
>+        for (let t of targets)
>+          t.style.width = "130px";
>+        a2.appendChild(b2);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "b2 moved downwards");
>+        assert_equals(entries[0].target, b2);
>+        a1.appendChild(a2);
>+      }
>+    },
>+  ]);
>+  return helper.start();
>+}
>+
>+let guard;
>+test(_ => {
>+  assert_own_property(window, "ResizeObserver");
>+  guard = async_test('guard');
>+}, "ResizeObserver implemented")
>+
>+test0()
>+  .then(() => { return test1(); })
>+  .then(() => { return test2(); })
>+  .then(() => { guard.done(); });
>+
>+</script>
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window-expected.txt
>new file mode 100644
>index 0000000000..a7ea32791c
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window-expected.txt
>@@ -0,0 +1,30 @@
>+
>+FAIL idl_test setup promise_test: Unhandled rejection with value: object "Got an error before parsing any named definition: Unrecognised tokens, line 1 (tokens: "{\"error\": {\"message\"")
>+[
>+    {
>+        "type": "{",
>+        "value": "{",
>+        "trivia": ""
>+    },
>+    {
>+        "type": "string",
>+        "value": "\"error\"",
>+        "trivia": ""
>+    },
>+    {
>+        "type": ":",
>+        "value": ":",
>+        "trivia": ""
>+    },
>+    {
>+        "type": "{",
>+        "value": "{",
>+        "trivia": " "
>+    },
>+    {
>+        "type": "string",
>+        "value": "\"message\"",
>+        "trivia": ""
>+    }
>+]"
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.html
>new file mode 100644
>index 0000000000..479d78c5ac
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.html
>@@ -0,0 +1,2 @@
>+
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.js b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.js
>new file mode 100644
>index 0000000000..592af2e0c0
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.js
>@@ -0,0 +1,37 @@
>+// META: script=/resources/WebIDLParser.js
>+// META: script=/resources/idlharness.js
>+// META: script=resources/resizeTestHelper.js
>+
>+'use strict';
>+
>+// https://wicg.github.io/ResizeObserver/
>+
>+idl_test(
>+  ['ResizeObserver'],
>+  ['dom', 'geometry'],
>+  async idl_array => {
>+    idl_array.add_objects({
>+      ResizeObserver: ['observer'],
>+      ResizeObserverEntry: ['entry'],
>+    });
>+
>+    const div = document.createElement('div');
>+    document.body.appendChild(div);
>+    let helper = new ResizeTestHelper(
>+      "ResizeObserverEntry creator",
>+      [
>+        {
>+          setup: observer => {
>+            self.observer = observer;
>+            observer.observe(div);
>+            div.style.width = "5px";
>+          },
>+          notify: entries => {
>+            self.entry = entries[0];
>+            assert_equals(entries[0].contentRect.width, 5, "target width");
>+          }
>+        }
>+      ]);
>+    await helper.start();
>+  }
>+);
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt
>new file mode 100644
>index 0000000000..0ea83587d1
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt
>@@ -0,0 +1,12 @@
>+ResizeObserver tests
>+
>+t1
>+t2
>+t3 inline
>+
>+Harness Error (TIMEOUT), message = null
>+
>+PASS ResizeObserver implemented 
>+NOTRUN guard 
>+FAIL test0: notification ordering assert_unreached: Timed out waiting for notification. (100ms) Reached unreachable code
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify.html
>new file mode 100644
>index 0000000000..b1038a3cb6
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify.html
>@@ -0,0 +1,351 @@
>+<!doctype html>
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="./resources/resizeTestHelper.js"></script>
>+<style>
>+  div {
>+    border: 1px dotted gray
>+  }
>+  .transform {
>+    transform: scale(2,2) rotate(90deg)
>+  }
>+</style>
>+<p>ResizeObserver tests</p>
>+<div id="target1" style="width:100px;height:100px;">t1
>+  <div id="target2" style="width:100px;height:100px;">t2
>+    <div id="target3" style="width:100px;height:100px;">t3
>+      <span id="inline">inline</span>
>+    </div>
>+  </div>
>+</div>
>+<div id="absolute" style="width:100.5px;height:100.5px;position:absolute;top:10.3px;left:10.3px"></div>
>+<script>
>+'use strict';
>+
>+let t1 = document.querySelector('#target1');
>+let t2 = document.querySelector('#target2');
>+let t3 = document.querySelector('#target3');
>+let abs = document.querySelector('#absolute');
>+let inline = document.querySelector('#inline');
>+
>+function test0() {
>+  let helper = new ResizeTestHelper(
>+    "test0: notification ordering",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t3);
>+        observer.observe(t2);
>+        observer.observe(t1);
>+        t1.style.width = "5px";
>+        t3.style.width = "5px";
>+        t2.style.width = "5px";
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 3, "3 resizes");
>+        assert_equals(entries[0].target, t3, "ordering");
>+        assert_equals(entries[1].target, t2, "ordering");
>+        assert_equals(entries[2].target, t1, "ordering");
>+        observer.disconnect();
>+        t1.style.width = "100px";
>+        t2.style.width = "100px";
>+        t3.style.width = "100px";
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test1() {
>+  let helper = new ResizeTestHelper(
>+    "test1: display:none triggers notification",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        t1.style.display = "none";
>+      },
>+      notify: (entries, observer) => {
>+        t1.style.display = "";
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+
>+function test2() {
>+  let helper = new ResizeTestHelper(
>+    "test2: remove/appendChild trigger notification",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    { // "removeChild triggers notification"
>+      setup: observer => {
>+        t1.parentNode.removeChild(t1);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries[0].target, t1);
>+        return true;  // Delay next step
>+      }
>+    },
>+    { // "appendChild triggers notification",
>+      setup: observer => {
>+        document.body.appendChild(t1);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries[0].target, t1)
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+
>+function test3() {
>+  let helper = new ResizeTestHelper(
>+    "test3: dimensions match",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        t1.style.width = "200.5px";
>+        t1.style.height = "100px";
>+        t1.style.paddingLeft = "20px";
>+        t1.style.paddingTop = "10px";
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries[0].contentRect.left,20);
>+        assert_equals(entries[0].contentRect.top,10);
>+        assert_between_inclusive(entries[0].contentRect.width, 200.4, 200.6, "width is not rounded");
>+        assert_equals(entries[0].contentRect.height, 100);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test4() {
>+  let helper = new ResizeTestHelper(
>+    "test4: transform do not cause notifications",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t2);
>+      },
>+      notify: (entries, observer) => {
>+        return true; // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        t2.classList.add("transform");
>+      },
>+      notify: (entries, observer) => {
>+        assert_unreached("transform must not trigger notifications");
>+      },
>+      timeout: () => {
>+        t2.classList.remove("transform");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test5() {
>+  let helper = new ResizeTestHelper(
>+    "test5: moving an element does not trigger notifications",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(abs);
>+      },
>+      notify: (entries, observer) => {
>+        return true; // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        abs.style.top = "20.33px";
>+        abs.style.left = "20.33px";
>+      },
>+      notify: (entries, observer) => {
>+        assert_unreached("movement should not cause resize notifications");
>+      },
>+      timeout: () => {
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test6() {
>+  let helper = new ResizeTestHelper(
>+    "test6: inline element does not notify",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(inline);
>+        observer.observe(t1);
>+        t1.style.width = "66px";
>+        inline.style.width = "66px";
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "inline elements must not trigger notifications");
>+        assert_equals(entries[0].target, t1, "inline elements must not trigger notifications");
>+        return true; // Delay next step
>+      }
>+    },
>+    { // "inline element that becomes block should notify",
>+      setup: observer => {
>+        inline.style.display = "block";
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries[0].target, inline);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test7() {
>+  let helper = new ResizeTestHelper(
>+    "test7: unobserve inside notify callback",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        observer.observe(t2);
>+      },
>+      notify: (entries, observer) => {
>+        t1.style.width = "777px";
>+        t2.style.width = "777px";
>+        observer.unobserve(t1);
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "only t2 is observed");
>+        assert_equals(entries[0].target, t2, "only t2 is observed");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test8() {
>+  let helper = new ResizeTestHelper(
>+    "test8: observe inside notify callback",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+      },
>+      notify: (entries, observer) => {
>+        observer.observe(t2);
>+        t2.style.width = "888px";
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1, "only t2 is observed");
>+        assert_equals(entries[0].target, t2, "only t2 is observed");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test9() {
>+  let helper = new ResizeTestHelper(
>+    "test9: disconnect inside notify callback",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+      },
>+      notify: (entries, observer) => {
>+        t1.style.width = "999px";
>+        observer.disconnect();
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+      },
>+      notify: (entries, observer) => {
>+        assert_unreached("there should be no notifications after disconnect");
>+      },
>+      timeout: () => {
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test10() {
>+  var parent = t1.parentNode;
>+  let helper = new ResizeTestHelper(
>+    "test10: element notifies when parent removed",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t3);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        t1.parentNode.removeChild(t1);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].target, t3);
>+        parent.appendChild(t1);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+let guard;
>+test(_ => {
>+  assert_own_property(window, "ResizeObserver");
>+  guard = async_test('guard');
>+}, "ResizeObserver implemented")
>+
>+test0()
>+  .then(() => { return test1(); })
>+  .then(() => { return test2(); })
>+  .then(() => { return test3(); })
>+  .then(() => { return test4(); })
>+  .then(() => { return test5(); })
>+  .then(() => { return test6(); })
>+  .then(() => { return test7(); })
>+  .then(() => { return test8(); })
>+  .then(() => { return test9(); })
>+  .then(() => { return test10(); })
>+  .then(() => { guard.done(); });
>+
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe-expected.txt
>new file mode 100644
>index 0000000000..d3e0b513a8
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe-expected.txt
>@@ -0,0 +1,12 @@
>+ResizeObserver tests
>+
>+t1
>+t2
>+ 
>+
>+Harness Error (TIMEOUT), message = null
>+
>+PASS ResizeObserver implemented 
>+NOTRUN guard 
>+FAIL test0: simple observation assert_unreached: Timed out waiting for notification. (100ms) Reached unreachable code
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe.html
>new file mode 100644
>index 0000000000..fc4592d459
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe.html
>@@ -0,0 +1,207 @@
>+<!doctype html>
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="./resources/resizeTestHelper.js"></script>
>+<p>ResizeObserver tests</p>
>+<div id="target1" style="width:100px;height:100px;">t1</div>
>+<div id="target2" style="width:100px;height:100px;">t2</div>
>+<img id="target3" style="width:100px;height:100px;">
>+<iframe src="./resources/iframe.html" width="300px" height="100px" style="display:block"></iframe>
>+<script>
>+'use strict';
>+
>+let t1 = document.querySelector('#target1');
>+let t2 = document.querySelector('#target2');
>+
>+// allow uncaught exception because ResizeObserver posts exceptions
>+// to window error handler when limit is exceeded.
>+setup({allow_uncaught_exception: true});
>+
>+function test0() {
>+  let helper = new ResizeTestHelper(
>+    "test0: simple observation",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        t1.style.width = "5px";
>+      },
>+      notify: entries => {
>+        assert_equals(entries.length, 1, "1 pending notification");
>+        assert_equals(entries[0].target, t1, "target is t1");
>+        assert_equals(entries[0].contentRect.width, 5, "target width");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test1() {
>+  let helper = new ResizeTestHelper(
>+    "test1: multiple observation on same element trigger only one",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        observer.observe(t1);
>+        t1.style.width = "10px";
>+      },
>+      notify: entries => {
>+        assert_equals(entries.length, 1, "1 pending notification");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test2() {
>+  test(() => {
>+      assert_throws({name: "TypeError"}, _=> {
>+        let ro = new ResizeObserver(() => {});
>+        ro.observe({});
>+      });
>+    },
>+    "test2: throw exception when observing non-element"
>+  );
>+  return Promise.resolve();
>+}
>+
>+function test3() {
>+  let helper = new ResizeTestHelper(
>+    "test3: disconnect stops all notifications", [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        observer.observe(t2);
>+        observer.disconnect();
>+        t1.style.width = "30px";
>+      },
>+      notify: entries => {
>+         assert_unreached("no entries should be observed");
>+      },
>+      timeout: () => {
>+        // expected
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test4() {
>+  let helper = new ResizeTestHelper(
>+    "test4: unobserve target stops notifications, unobserve non-observed does nothing", [
>+    {
>+      setup: observer => {
>+        observer.observe(t1);
>+        observer.observe(t2);
>+        observer.unobserve(t1);
>+        observer.unobserve(document.body);
>+        t1.style.width = "40px";
>+        t2.style.width = "40px";
>+      },
>+      notify: entries => {
>+        assert_equals(entries.length, 1, "only t2");
>+        assert_equals(entries[0].target, t2, "t2 was observed");
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test5() {
>+  let t3 = document.querySelector('#target3');
>+  var helper = new ResizeTestHelper("test5: observe img",[
>+    {
>+      setup: observer => {
>+        observer.observe(t3);
>+      },
>+      notify: entries => {
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        t3.style.width = "100.5px";
>+      },
>+      notify: entries => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 100.5);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test6() {
>+  let resolvePromise;
>+  let promise = new Promise((resolve) => {
>+    resolvePromise = resolve;
>+  });
>+  let test = async_test('test6: iframe notifications');
>+  let testRequested = false;
>+  let iframe = document.querySelector('iframe');
>+  window.addEventListener('message', event => {
>+    switch(event.data) {
>+    case 'readyToTest':
>+      if (!testRequested) {
>+        iframe.contentWindow.postMessage('startTest', '*');
>+        testRequested = true;
>+      }
>+    break;
>+    case 'success':
>+    case 'fail':
>+      window.requestAnimationFrame(() => {
>+        test.step( () => {
>+          assert_equals(event.data, 'success');
>+          test.done();
>+          resolvePromise();
>+        });
>+      });
>+    break;
>+    }
>+  }, false);
>+  return promise;
>+}
>+
>+function test7() {
>+  let harnessTest = async_test("test7: callback.this");
>+  let resolvePromise;
>+  let ro = new ResizeObserver( function(entries, obs)  {
>+    let callbackThis = this;
>+    resolvePromise();
>+    harnessTest.step(() => {
>+      assert_equals(callbackThis, ro, "callback.this is ResizeObserver");
>+      assert_equals(obs, ro, "2nd argument is ResizeObserver");
>+      ro.disconnect();
>+      // every reference to RO must be null before test completes
>+      // to avoid triggering test leak-detection
>+      ro = null;
>+      callbackThis = null;
>+      obs = null;
>+      harnessTest.done();
>+     });
>+    }
>+  );
>+  ro.observe(t1);
>+
>+  return new Promise( (resolve, reject) => {
>+    resolvePromise = resolve;
>+  });
>+}
>+
>+let guard;
>+test(_ => {
>+  assert_own_property(window, "ResizeObserver");
>+  guard = async_test('guard');
>+}, "ResizeObserver implemented")
>+
>+test0()
>+  .then(() => { return test1(); })
>+  .then(() => { return test2(); })
>+  .then(() => { return test3(); })
>+  .then(() => { return test4(); })
>+  .then(() => { return test5(); })
>+  .then(() => { return test6(); })
>+  .then(() => { return test7(); })
>+  .then(() => { guard.done(); });
>+
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/iframe.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/iframe.html
>new file mode 100644
>index 0000000000..518317b520
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/iframe.html
>@@ -0,0 +1,38 @@
>+<!doctype html>
>+<head>
>+  <script src="./resizeTestHelper.js"></script>
>+</head>
>+<p>iframe test</p>
>+<div id="itarget1" style="width:100px;height:100px;">t1</div>
>+<script>
>+'use strict';
>+let t1 = document.querySelector('#itarget1');
>+function test0() {
>+  let timeoutId = window.setTimeout( () => {
>+    window.parent.postMessage('fail', '*');
>+  }, ResizeTestHelper.TIMEOUT);
>+  let ro = new ResizeObserver(function(entries) {
>+    window.clearTimeout(timeoutId);
>+    window.parent.postMessage('success', '*');
>+  });
>+  ro.observe(t1);
>+}
>+let testStarted = false;
>+window.addEventListener('message', function(ev) {
>+    switch(ev.data) {
>+        case 'startTest':
>+          testStarted = true;
>+          test0();
>+        break;
>+    }
>+});
>+// How does parent know we've loaded problem is solved by
>+// broadcasting readyToTest message repeatedly until test starts.
>+function broadcastReady() {
>+  if (!testStarted) {
>+    window.parent.postMessage('readyToTest', '*');
>+    window.requestAnimationFrame(broadcastReady);
>+  }
>+}
>+broadcastReady();
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/resizeTestHelper.js b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/resizeTestHelper.js
>new file mode 100644
>index 0000000000..60c681bd93
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/resizeTestHelper.js
>@@ -0,0 +1,148 @@
>+'use strict';
>+
>+/**
>+  ResizeTestHelper is a framework to test ResizeObserver
>+  notifications. Use it to make assertions about ResizeObserverEntries.
>+  This framework is needed because ResizeObservations are
>+  delivered asynchronously inside the event loop.
>+
>+  Features:
>+  - can queue multiple notification steps in a test
>+  - handles timeouts
>+  - returns Promise that is fullfilled when test completes.
>+    Use to chain tests (since parallel async ResizeObserver tests
>+    would conflict if reusing same DOM elements).
>+
>+  Usage:
>+
>+  create ResizeTestHelper for every test.
>+  Make assertions inside notify, timeout callbacks.
>+  Start tests with helper.start()
>+  Chain tests with Promises.
>+  Counts animation frames, see startCountingRaf
>+*/
>+
>+/*
>+  @param name: test name
>+  @param steps:
>+  {
>+    setup: function(ResizeObserver) {
>+      // called at the beginning of the test step
>+      // your observe/resize code goes here
>+    },
>+    notify: function(entries, observer) {
>+      // ResizeObserver callback.
>+      // Make assertions here.
>+      // Return true if next step should start on the next event loop.
>+    },
>+    timeout: function() {
>+      // Define this if your test expects to time out.
>+      // If undefined, timeout is assert_unreached.
>+    }
>+  }
>+*/
>+function ResizeTestHelper(name, steps)
>+{
>+    this._name = name;
>+    this._steps = steps || [];
>+    this._stepIdx = -1;
>+    this._harnessTest = null;
>+    this._observer = new ResizeObserver(this._handleNotification.bind(this));
>+    this._timeoutBind = this._handleTimeout.bind(this);
>+    this._nextStepBind = this._nextStep.bind(this);
>+}
>+
>+ResizeTestHelper.TIMEOUT = 100;
>+
>+ResizeTestHelper.prototype = {
>+  get _currentStep() {
>+    return this._steps[this._stepIdx];
>+  },
>+
>+  _nextStep: function() {
>+    if (++this._stepIdx == this._steps.length)
>+      return this._done();
>+    this._timeoutId = this._harnessTest.step_timeout(
>+      this._timeoutBind, ResizeTestHelper.TIMEOUT);
>+    try {
>+      this._steps[this._stepIdx].setup(this._observer);
>+    }
>+    catch(err) {
>+      this._harnessTest.step(() => {
>+        assert_unreached("Caught a throw, possible syntax error");
>+      });
>+    }
>+  },
>+
>+  _handleNotification: function(entries) {
>+    if (this._timeoutId) {
>+      window.clearTimeout(this._timeoutId);
>+      delete this._timeoutId;
>+    }
>+    this._harnessTest.step(() => {
>+      let rafDelay = this._currentStep.notify(entries, this._observer);
>+      if (rafDelay)
>+        window.requestAnimationFrame(this._nextStepBind);
>+      else
>+        this._nextStep();
>+    });
>+  },
>+
>+  _handleTimeout: function() {
>+    delete this._timeoutId;
>+    this._harnessTest.step(() => {
>+      if (this._currentStep.timeout) {
>+        this._currentStep.timeout();
>+      }
>+      else {
>+        assert_unreached("Timed out waiting for notification. (" + ResizeTestHelper.TIMEOUT + "ms)");
>+      }
>+      this._nextStep();
>+    });
>+  },
>+
>+  _done: function() {
>+    this._observer.disconnect();
>+    delete this._observer;
>+    this._harnessTest.done();
>+    if (this._rafCountRequest) {
>+      window.cancelAnimationFrame(this._rafCountRequest);
>+      delete this._rafCountRequest;
>+    }
>+    window.requestAnimationFrame(() => { this._resolvePromise(); });
>+  },
>+
>+  start: function() {
>+    this._harnessTest = async_test(this._name);
>+    this._harnessTest.step(() => {
>+      assert_equals(this._stepIdx, -1, "start can only be called once");
>+      this._nextStep();
>+    });
>+    return new Promise( (resolve, reject) => {
>+      this._resolvePromise = resolve;
>+      this._rejectPromise = reject;
>+    });
>+  },
>+
>+  get rafCount() {
>+    if (!this._rafCountRequest)
>+      throw "rAF count is not active";
>+    return this._rafCount;
>+  },
>+
>+  _incrementRaf: function() {
>+    if (this._rafCountRequest) {
>+      this._rafCount++;
>+      this._rafCountRequest = window.requestAnimationFrame(this._incrementRafBind);
>+    }
>+  },
>+
>+  startCountingRaf: function() {
>+    if (this._rafCountRequest)
>+      window.cancelAnimationFrame(this._rafCountRequest);
>+    if (!this._incrementRafBind)
>+      this._incrementRafBind = this._incrementRaf.bind(this);
>+    this._rafCount = 0;
>+    this._rafCountRequest = window.requestAnimationFrame(this._incrementRafBind);
>+  }
>+}
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/w3c-import.log b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/w3c-import.log
>new file mode 100644
>index 0000000000..af37cea5fc
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/w3c-import.log
>@@ -0,0 +1,18 @@
>+The tests in this directory were imported from the W3C repository.
>+Do NOT modify these tests directly in WebKit.
>+Instead, create a pull request on the WPT github:
>+	https://github.com/web-platform-tests/wpt
>+
>+Then run the Tools/Scripts/import-w3c-tests in WebKit to reimport
>+
>+Do NOT modify or remove this file.
>+
>+------------------------------------------------------------------------
>+Properties requiring vendor prefixes:
>+None
>+Property values requiring vendor prefixes:
>+None
>+------------------------------------------------------------------------
>+List of files:
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/iframe.html
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/resources/resizeTestHelper.js
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt
>new file mode 100644
>index 0000000000..c4483ea7ce
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt
>@@ -0,0 +1,12 @@
>+ResizeObserver svg tests
>+
>+Here is a paragraph that requires word wrap
>+
>+svg text tag
>+
>+Harness Error (TIMEOUT), message = null
>+
>+PASS ResizeObserver implemented 
>+NOTRUN guard 
>+FAIL test0: observe svg:circle assert_unreached: Timed out waiting for notification. (100ms) Reached unreachable code
>+
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg.html b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg.html
>new file mode 100644
>index 0000000000..49e5c1953e
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg.html
>@@ -0,0 +1,333 @@
>+<!doctype html>
>+<script src="/resources/testharness.js"></script>
>+<script src="/resources/testharnessreport.js"></script>
>+<script src="./resources/resizeTestHelper.js"></script>
>+<p>ResizeObserver svg tests</p>
>+<svg height="430" width="500" >
>+  <circle cx="10" cy="10" r="5" style="fill:orange;stroke:black;stroke-width:1" />
>+  <ellipse cx="10" cy="30" rx="5" ry="5" style="fill:orange;stroke:black;stroke-width:1"/>
>+  <foreignObject cy="50" width="100" height="20">
>+    <body>
>+      <p>Here is a paragraph that requires word wrap</p>
>+    </body>
>+  </foreignObject>
>+  <image xlink:href="" x="0" y="100" height="30" width="100" />
>+  <line x1="0" y1="50" x2="20" y2="70" stroke="black" stroke-width="2"/>
>+  <path d="M 0 100 L 100 100 L 50 150 z"
>+        style="fill:orange;stroke:black;stroke-width:1" />
>+  <polygon points="0,200 100,200 50,250" style="fill:orange;stroke:black;stroke-width:1" />
>+  <polyline points="0,300 100,300 50,350" style="fill:orange;stroke:black;stroke-width:1"/>
>+  <rect x="0" y="380" width="10" height="10" style="fill:orange; stroke:black; stroke-width:1" />
>+  <text x="0" y="400" font-size="20">svg text tag</text>
>+</svg>
>+<script>
>+'use strict';
>+
>+setup({allow_uncaught_exception: true});
>+
>+function test0() {
>+  let target = document.querySelector('circle');
>+  let helper = new ResizeTestHelper(
>+    "test0: observe svg:circle",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('r', 10);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test1() {
>+  let target = document.querySelector('ellipse');
>+  let helper = new ResizeTestHelper(
>+    "test1: observe svg:ellipse",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('rx', 10);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 20);
>+        assert_equals(entries[0].contentRect.height, 10);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test2() {
>+  let target = document.querySelector('foreignObject');
>+  let helper = new ResizeTestHelper(
>+    "test2: observe svg:foreignObject",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('width', 200);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 200);
>+        assert_equals(entries[0].contentRect.height, 20);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test3() {
>+  let target = document.querySelector('image');
>+  let helper = new ResizeTestHelper(
>+    "test3: observe svg:image",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('height', 40);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 100);
>+        assert_equals(entries[0].contentRect.height, 40);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test4() {
>+  let target = document.querySelector('line');
>+  let helper = new ResizeTestHelper(
>+    "test4: observe svg:line",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('y2', 80);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 20);
>+        assert_equals(entries[0].contentRect.height, 30);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test5() {
>+  let target = document.querySelector('path');
>+  let helper = new ResizeTestHelper(
>+    "test5: observe svg:path",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('d', "M 0 100 L 100 100 L 50 160 z");
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 100);
>+        assert_equals(entries[0].contentRect.height, 60);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test6() {
>+  let target = document.querySelector('polygon');
>+  let helper = new ResizeTestHelper(
>+    "test6: observe svg:path",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('points', "0,200 100,200 50,260");
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 100);
>+        assert_equals(entries[0].contentRect.height, 60);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test7() {
>+  let target = document.querySelector('polyline');
>+  let helper = new ResizeTestHelper(
>+    "test7: observe svg:polyline",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('points', "0,300 100,300 50,360");
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 100);
>+        assert_equals(entries[0].contentRect.height, 60);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test8() {
>+  let target = document.querySelector('rect');
>+  let helper = new ResizeTestHelper(
>+    "test8: observe svg:rect",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('width', "20");
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.width, 20);
>+        assert_equals(entries[0].contentRect.height, 10);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+function test9() {
>+  let target = document.querySelector('text');
>+  let helper = new ResizeTestHelper(
>+    "test9: observe svg:text",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        return true;  // Delay next step
>+      }
>+    },
>+    {
>+      setup: observer => {
>+        target.setAttribute('font-size', "25");
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+
>+function test10() {
>+  let target = document.querySelector('svg');
>+  let helper = new ResizeTestHelper(
>+    "test10: observe svg:svg, top/left is 0 even with padding",
>+  [
>+    {
>+      setup: observer => {
>+        observer.observe(target);
>+      },
>+      notify: (entries, observer) => {
>+        assert_equals(entries.length, 1);
>+        assert_equals(entries[0].contentRect.top, 0);
>+        assert_equals(entries[0].contentRect.left, 0);
>+      }
>+    }
>+  ]);
>+  return helper.start();
>+}
>+
>+let guard;
>+test(_ => {
>+  assert_own_property(window, "ResizeObserver");
>+  guard = async_test('guard');
>+}, "ResizeObserver implemented")
>+
>+test0()
>+  .then(() => { return test1(); })
>+  .then(() => { return test2(); })
>+  .then(() => { return test3(); })
>+  .then(() => { return test4(); })
>+  .then(() => { return test5(); })
>+  .then(() => { return test6(); })
>+  .then(() => { return test7(); })
>+  .then(() => { return test8(); })
>+  .then(() => { return test9(); })
>+  .then(() => { return test10(); })
>+  .then(() => { guard.done(); });
>+
>+</script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/resize-observer/w3c-import.log b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/w3c-import.log
>new file mode 100644
>index 0000000000..5641eec2c8
>--- /dev/null
>+++ b/LayoutTests/imported/w3c/web-platform-tests/resize-observer/w3c-import.log
>@@ -0,0 +1,22 @@
>+The tests in this directory were imported from the W3C repository.
>+Do NOT modify these tests directly in WebKit.
>+Instead, create a pull request on the WPT github:
>+	https://github.com/web-platform-tests/wpt
>+
>+Then run the Tools/Scripts/import-w3c-tests in WebKit to reimport
>+
>+Do NOT modify or remove this file.
>+
>+------------------------------------------------------------------------
>+Properties requiring vendor prefixes:
>+None
>+Property values requiring vendor prefixes:
>+None
>+------------------------------------------------------------------------
>+List of files:
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/META.yml
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/eventloop.html
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/idlharness.window.js
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify.html
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe.html
>+/LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg.html
>diff --git a/Source/WebCore/CMakeLists.txt b/Source/WebCore/CMakeLists.txt
>index 482cf6fd59..8147f7e771 100644
>--- a/Source/WebCore/CMakeLists.txt
>+++ b/Source/WebCore/CMakeLists.txt
>@@ -925,6 +925,9 @@ set(WebCore_NON_SVG_IDL_FILES
>     page/PerformanceServerTiming.idl
>     page/PerformanceTiming.idl
>     page/RemoteDOMWindow.idl
>+    page/ResizeObserver.idl
>+    page/ResizeObserverCallback.idl
>+    page/ResizeObserverEntry.idl
>     page/Screen.idl
>     page/ScrollIntoViewOptions.idl
>     page/ScrollLogicalPosition.idl
>diff --git a/Source/WebCore/DerivedSources.make b/Source/WebCore/DerivedSources.make
>index cd6757664e..556629cb81 100644
>--- a/Source/WebCore/DerivedSources.make
>+++ b/Source/WebCore/DerivedSources.make
>@@ -873,6 +873,9 @@ JS_BINDING_IDLS = \
>     $(WebCore)/page/PerformanceServerTiming.idl \
>     $(WebCore)/page/PerformanceTiming.idl \
>     $(WebCore)/page/RemoteDOMWindow.idl \
>+    $(WebCore)/page/ResizeObserver.idl \
>+    $(WebCore)/page/ResizeObserverCallback.idl \
>+    $(WebCore)/page/ResizeObserverEntry.idl \
>     $(WebCore)/page/Screen.idl \
>     $(WebCore)/page/ScrollIntoViewOptions.idl \
>     $(WebCore)/page/ScrollLogicalPosition.idl \
>diff --git a/Source/WebCore/Sources.txt b/Source/WebCore/Sources.txt
>index de5421f8f8..e98a855000 100644
>--- a/Source/WebCore/Sources.txt
>+++ b/Source/WebCore/Sources.txt
>@@ -1529,6 +1529,8 @@ page/ProcessWarming.cpp
> page/Quirks.cpp
> page/RemoteDOMWindow.cpp
> page/RemoteFrame.cpp
>+page/ResizeObservation.cpp
>+page/ResizeObserver.cpp
> page/ResourceUsageOverlay.cpp
> page/ResourceUsageThread.cpp
> page/RuntimeEnabledFeatures.cpp
>diff --git a/Source/WebCore/bindings/js/WebCoreBuiltinNames.h b/Source/WebCore/bindings/js/WebCoreBuiltinNames.h
>index 183fe8a885..a0a2265d6a 100644
>--- a/Source/WebCore/bindings/js/WebCoreBuiltinNames.h
>+++ b/Source/WebCore/bindings/js/WebCoreBuiltinNames.h
>@@ -145,6 +145,8 @@ namespace WebCore {
>     macro(PerformanceServerTiming) \
>     macro(PointerEvent) \
>     macro(PublicKeyCredential) \
>+    macro(ResizeObserver) \
>+    macro(ResizeObserverEntry) \
>     macro(RTCCertificate) \
>     macro(RTCDTMFSender) \
>     macro(RTCDTMFToneChangeEvent) \
>diff --git a/Source/WebCore/dom/Document.cpp b/Source/WebCore/dom/Document.cpp
>index 6d443e7866..91d9d2eb3e 100644
>--- a/Source/WebCore/dom/Document.cpp
>+++ b/Source/WebCore/dom/Document.cpp
>@@ -161,6 +161,7 @@
> #include "RenderView.h"
> #include "RenderWidget.h"
> #include "RequestAnimationFrameCallback.h"
>+#include "ResizeObserver.h"
> #include "ResourceLoadObserver.h"
> #include "RuntimeApplicationChecks.h"
> #include "RuntimeEnabledFeatures.h"
>@@ -8035,6 +8036,19 @@ void Document::notifyIntersectionObserversTimerFired()
> }
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+void Document::addResizeObserver(ResizeObserver& observer)
>+{
>+    ASSERT(m_resizeObservers.find(&observer) == notFound);
>+    m_resizeObservers.append(makeWeakPtr(&observer));
>+}
>+
>+void Document::removeResizeObserver(ResizeObserver& observer)
>+{
>+    m_resizeObservers.removeFirst(&observer);
>+}
>+#endif
>+
> const AtomicString& Document::dir() const
> {
>     auto* documentElement = this->documentElement();
>diff --git a/Source/WebCore/dom/Document.h b/Source/WebCore/dom/Document.h
>index 30f0ee67c9..fda1905380 100644
>--- a/Source/WebCore/dom/Document.h
>+++ b/Source/WebCore/dom/Document.h
>@@ -246,6 +246,10 @@ class HTMLAttachmentElement;
> class IntersectionObserver;
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+class ResizeObserver;
>+#endif
>+
> namespace Style {
> class Scope;
> };
>@@ -1416,6 +1420,11 @@ public:
>     void updateIntersectionObservations();
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    void addResizeObserver(ResizeObserver&);
>+    void removeResizeObserver(ResizeObserver&);
>+#endif
>+
> #if ENABLE(MEDIA_STREAM)
>     void setHasCaptureMediaStreamTrack() { m_hasHadCaptureMediaStreamTrack = true; }
>     bool hasHadCaptureMediaStreamTrack() const { return m_hasHadCaptureMediaStreamTrack; }
>@@ -1862,6 +1871,10 @@ private:
>     Timer m_intersectionObserversNotifyTimer;
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    Vector<WeakPtr<ResizeObserver>> m_resizeObservers;
>+#endif
>+
>     Timer m_loadEventDelayTimer;
> 
>     ViewportArguments m_viewportArguments;
>diff --git a/Source/WebCore/dom/Element.cpp b/Source/WebCore/dom/Element.cpp
>index ea5493a5a2..1d6cdf6245 100644
>--- a/Source/WebCore/dom/Element.cpp
>+++ b/Source/WebCore/dom/Element.cpp
>@@ -194,6 +194,10 @@ Element::~Element()
>     disconnectFromIntersectionObservers();
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    disconnectFromResizeObservers();
>+#endif
>+
>     removeShadowRoot();
> 
>     if (hasSyntheticAttrChildNodes())
>@@ -1837,6 +1841,10 @@ void Element::didMoveToNewDocument(Document& oldDocument, Document& newDocument)
>         }
>     }
> #endif
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+    disconnectFromResizeObservers();
>+#endif
> }
> 
> bool Element::hasAttributes() const
>@@ -3470,6 +3478,32 @@ IntersectionObserverData* Element::intersectionObserverData()
> }
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+void Element::disconnectFromResizeObservers()
>+{
>+    auto* observerData = resizeObserverData();
>+    if (!observerData)
>+        return;
>+
>+    for (const auto& observer : observerData->observers)
>+        observer->targetDestroyed(*this);
>+    observerData->observers.clear();
>+}
>+
>+ResizeObserverData& Element::ensureResizeObserverData()
>+{
>+    auto& rareData = ensureElementRareData();
>+    if (!rareData.resizeObserverData())
>+        rareData.setResizeObserverData(std::make_unique<ResizeObserverData>());
>+    return *rareData.resizeObserverData();
>+}
>+
>+ResizeObserverData* Element::resizeObserverData()
>+{
>+    return hasRareData() ? elementRareData()->resizeObserverData() : nullptr;
>+}
>+#endif
>+
> SpellcheckAttributeState Element::spellcheckAttributeState() const
> {
>     const AtomicString& value = attributeWithoutSynchronization(HTMLNames::spellcheckAttr);
>diff --git a/Source/WebCore/dom/Element.h b/Source/WebCore/dom/Element.h
>index c5eb6cb8c4..d080dd290c 100644
>--- a/Source/WebCore/dom/Element.h
>+++ b/Source/WebCore/dom/Element.h
>@@ -63,6 +63,10 @@ struct ScrollIntoViewOptions;
> struct IntersectionObserverData;
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+struct ResizeObserverData;
>+#endif
>+
> enum SpellcheckAttributeState {
>     SpellcheckAttributeTrue,
>     SpellcheckAttributeFalse,
>@@ -583,6 +587,11 @@ public:
>     IntersectionObserverData* intersectionObserverData();
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    ResizeObserverData& ensureResizeObserverData();
>+    ResizeObserverData* resizeObserverData();
>+#endif
>+
>     Element* findAnchorElementForLink(String& outAnchorName);
> 
>     ExceptionOr<Ref<WebAnimation>> animate(JSC::ExecState&, JSC::Strong<JSC::JSObject>&&, Optional<Variant<double, KeyframeAnimationOptions>>&&);
>@@ -669,6 +678,10 @@ private:
>     void disconnectFromIntersectionObservers();
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    void disconnectFromResizeObservers();
>+#endif
>+
>     // The cloneNode function is private so that non-virtual cloneElementWith/WithoutChildren are used instead.
>     Ref<Node> cloneNodeInternal(Document&, CloningOperation) override;
>     virtual Ref<Element> cloneElementWithoutAttributesAndChildren(Document&);
>diff --git a/Source/WebCore/dom/ElementRareData.cpp b/Source/WebCore/dom/ElementRareData.cpp
>index 4dd60eb84f..140b898900 100644
>--- a/Source/WebCore/dom/ElementRareData.cpp
>+++ b/Source/WebCore/dom/ElementRareData.cpp
>@@ -50,6 +50,9 @@ struct SameSizeAsElementRareData : NodeRareData {
> #if ENABLE(CSS_TYPED_OM)
>     void* typedOMData;
> #endif
>+#if ENABLE(RESIZE_OBSERVER)
>+    void* resizeObserverData;
>+#endif
> 
> };
> 
>diff --git a/Source/WebCore/dom/ElementRareData.h b/Source/WebCore/dom/ElementRareData.h
>index fe80e331d5..8e106fb8a5 100644
>--- a/Source/WebCore/dom/ElementRareData.h
>+++ b/Source/WebCore/dom/ElementRareData.h
>@@ -29,6 +29,7 @@
> #include "NodeRareData.h"
> #include "PseudoElement.h"
> #include "RenderElement.h"
>+#include "ResizeObserver.h"
> #include "ShadowRoot.h"
> #include "StylePropertyMap.h"
> 
>@@ -128,6 +129,11 @@ public:
>     void setIntersectionObserverData(std::unique_ptr<IntersectionObserverData>&& data) { m_intersectionObserverData = WTFMove(data); }
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    ResizeObserverData* resizeObserverData() { return m_resizeObserverData.get(); }
>+    void setResizeObserverData(std::unique_ptr<ResizeObserverData>&& data) { m_resizeObserverData = WTFMove(data); }
>+#endif
>+
> #if ENABLE(CSS_TYPED_OM)
>     StylePropertyMap* attributeStyleMap() { return m_attributeStyleMap.get(); }
>     void setAttributeStyleMap(Ref<StylePropertyMap>&& map) { m_attributeStyleMap = WTFMove(map); }
>@@ -162,6 +168,8 @@ public:
>             result.add(UseType::AttributeMap);
>         if (m_intersectionObserverData)
>             result.add(UseType::InteractionObserver);
>+        if (m_resizeObserverData)
>+            result.add(UseType::ResizeObserver);
>         if (m_beforePseudoElement || m_afterPseudoElement)
>             result.add(UseType::PseudoElements);
>         return result;
>@@ -205,6 +213,10 @@ private:
>     std::unique_ptr<IntersectionObserverData> m_intersectionObserverData;
> #endif
> 
>+#if ENABLE(RESIZE_OBSERVER)
>+    std::unique_ptr<ResizeObserverData> m_resizeObserverData;
>+#endif
>+
>     RefPtr<PseudoElement> m_beforePseudoElement;
>     RefPtr<PseudoElement> m_afterPseudoElement;
> 
>diff --git a/Source/WebCore/page/ResizeObservation.cpp b/Source/WebCore/page/ResizeObservation.cpp
>new file mode 100644
>index 0000000000..f0882d3d19
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObservation.cpp
>@@ -0,0 +1,50 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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"
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+#include "ResizeObservation.h"
>+
>+namespace WebCore {
>+
>+ResizeObservation::ResizeObservation(Element* element)
>+    : m_target(element)
>+    , m_observationSize(0, 0)
>+{
>+}
>+
>+ResizeObservation::~ResizeObservation()
>+{
>+}
>+
>+void ResizeObservation::setObservationSize(const LayoutSize& size)
>+{
>+    m_observationSize = size;
>+}
>+
>+} // namespace WebCore
>+
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObservation.h b/Source/WebCore/page/ResizeObservation.h
>new file mode 100644
>index 0000000000..789e6a3d71
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObservation.h
>@@ -0,0 +1,55 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+#include "LayoutSize.h"
>+
>+#include <wtf/RefCounted.h>
>+
>+namespace WebCore {
>+
>+class Element;
>+
>+class ResizeObservation : public RefCounted<ResizeObservation> {
>+    WTF_MAKE_FAST_ALLOCATED;
>+public:
>+    ResizeObservation(Element* target);
>+    ~ResizeObservation();
>+    void setObservationSize(const LayoutSize&);
>+    Element* target() { return m_target; }
>+    LayoutSize observationSize() { return m_observationSize; }
>+
>+private:
>+
>+    Element* m_target;
>+    // target size in last observation
>+    LayoutSize m_observationSize;
>+};
>+
>+} // namespace WebCore
>+
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObserver.cpp b/Source/WebCore/page/ResizeObserver.cpp
>new file mode 100644
>index 0000000000..ead9861f40
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserver.cpp
>@@ -0,0 +1,146 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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"
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+#include "ResizeObserver.h"
>+
>+#include "Element.h"
>+
>+namespace WebCore {
>+Ref<ResizeObserver> ResizeObserver::create(Document& document, Ref<ResizeObserverCallback>&& callback)
>+{
>+    return WTF::adoptRef(*new ResizeObserver(document, WTFMove(callback)));
>+}
>+
>+ResizeObserver::ResizeObserver(Document& document, Ref<ResizeObserverCallback>&& callback)
>+    : ActiveDOMObject(downcast<Document>(callback->scriptExecutionContext()))
>+    , m_callback(WTFMove(callback))
>+{
>+    m_document = makeWeakPtr(document);
>+    suspendIfNeeded();
>+}
>+
>+ResizeObserver::~ResizeObserver()
>+{
>+    disconnect();
>+}
>+
>+void ResizeObserver::observe(Element& target)
>+{
>+    if (!m_callback)
>+        return;
>+
>+    for (auto observation : m_observations) {
>+        if (observation->target() == &target)
>+            return;
>+    }
>+
>+    auto& observerData = target.ensureResizeObserverData();
>+    observerData.observers.append(makeWeakPtr(this));
>+    if (!hasObservations())
>+        m_document->addResizeObserver(*this);
>+
>+    m_observations.append(WTF::adoptRef(new ResizeObservation(&target)));
>+
>+}
>+
>+void ResizeObserver::unobserve(Element& target)
>+{
>+    if (!removeTarget(target))
>+        return;
>+
>+    removeObservation(target);
>+
>+    if (!hasObservations())
>+        m_document->removeResizeObserver(*this);
>+
>+}
>+
>+void ResizeObserver::disconnect()
>+{
>+    removeAllTargets();
>+    m_document->removeResizeObserver(*this);
>+}
>+
>+void ResizeObserver::removeAllTargets()
>+{
>+    for (auto observation : m_observations) {
>+        bool removed = removeTarget(*observation->target());
>+        ASSERT_UNUSED(removed, removed);
>+    }
>+    m_observations.clear();
>+}
>+
>+bool ResizeObserver::removeTarget(Element& target)
>+{
>+    auto* observerData = target.resizeObserverData();
>+    if (!observerData)
>+        return false;
>+
>+    auto& observers = observerData->observers;
>+    return observers.removeFirst(this);
>+}
>+
>+void ResizeObserver::targetDestroyed(Element& target)
>+{
>+    removeObservation(target);
>+    if (!hasObservations())
>+        m_document->removeResizeObserver(*this);
>+}
>+
>+bool ResizeObserver::removeObservation(Element& target)
>+{
>+    return m_observations.removeFirstMatching([&target](auto& observation) {
>+        return observation->target() == &target;
>+    });
>+}
>+
>+bool ResizeObserver::hasPendingActivity() const
>+{
>+    // TODO: cc. Need add the conditions when ResizeObserver is complete.
>+    return hasObservations() && m_document;
>+}
>+
>+const char* ResizeObserver::activeDOMObjectName() const
>+{
>+    return "ResizeObserver";
>+}
>+
>+bool ResizeObserver::canSuspendForDocumentSuspension() const
>+{
>+    return true;
>+}
>+
>+void ResizeObserver::stop()
>+{
>+    disconnect();
>+    m_callback = nullptr;
>+}
>+
>+} // namespace WebCore
>+
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObserver.h b/Source/WebCore/page/ResizeObserver.h
>new file mode 100644
>index 0000000000..c5e2eb12ed
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserver.h
>@@ -0,0 +1,80 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+
>+#include "ActiveDOMObject.h"
>+#include "ResizeObservation.h"
>+#include "ResizeObserverCallback.h"
>+#include <wtf/RefCounted.h>
>+#include <wtf/WeakPtr.h>
>+
>+namespace WebCore {
>+
>+class Document;
>+class Element;
>+
>+struct ResizeObserverData {
>+    Vector<WeakPtr<ResizeObserver>> observers;
>+};
>+
>+class ResizeObserver : public RefCounted<ResizeObserver>, public ActiveDOMObject, public CanMakeWeakPtr<ResizeObserver> {
>+    WTF_MAKE_FAST_ALLOCATED;
>+public:
>+    static Ref<ResizeObserver> create(Document&, Ref<ResizeObserverCallback>&&);
>+    ~ResizeObserver();
>+
>+    const Vector<RefPtr<ResizeObservation>> observations() const { return m_observations; }
>+    bool hasObservations() const { return m_observations.size(); }
>+
>+    void observe(Element&);
>+    void unobserve(Element&);
>+    void disconnect();
>+
>+    void targetDestroyed(Element&);
>+
>+    // ActiveDOMObject.
>+    bool hasPendingActivity() const override;
>+    const char* activeDOMObjectName() const override;
>+    bool canSuspendForDocumentSuspension() const override;
>+    void stop() override;
>+
>+private:
>+    ResizeObserver(Document&, Ref<ResizeObserverCallback>&&);
>+
>+    void removeAllTargets();
>+    bool removeTarget(Element&);
>+    bool removeObservation(Element&);
>+
>+    WeakPtr<Document> m_document;
>+    RefPtr<ResizeObserverCallback> m_callback;
>+    Vector<RefPtr<ResizeObservation>> m_observations;
>+};
>+
>+} // namespace WebCore
>+
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObserver.idl b/Source/WebCore/page/ResizeObserver.idl
>new file mode 100644
>index 0000000000..87f80106ad
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserver.idl
>@@ -0,0 +1,38 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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.
>+ */
>+
>+// https://wicg.github.io/ResizeObserver/
>+
>+[
>+    ActiveDOMObject,
>+    Conditional=RESIZE_OBSERVER,
>+    Constructor(ResizeObserverCallback callback),
>+    ConstructorCallWith=Document,
>+    EnabledBySetting=ResizeObserver
>+] interface ResizeObserver {
>+    void observe(Element target);
>+    void unobserve(Element target);
>+    void disconnect();
>+};
>diff --git a/Source/WebCore/page/ResizeObserverCallback.h b/Source/WebCore/page/ResizeObserverCallback.h
>new file mode 100644
>index 0000000000..b39d7626f6
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserverCallback.h
>@@ -0,0 +1,47 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+
>+#include "ActiveDOMCallback.h"
>+#include "CallbackResult.h"
>+#include <wtf/RefCounted.h>
>+
>+namespace WebCore {
>+
>+class ResizeObserver;
>+class ResizeObserverEntry;
>+
>+class ResizeObserverCallback : public RefCounted<ResizeObserverCallback>, public ActiveDOMCallback {
>+public:
>+    using ActiveDOMCallback::ActiveDOMCallback;
>+    virtual CallbackResult<void> handleEvent(const Vector<Ref<ResizeObserverEntry>>&, ResizeObserver&) = 0;
>+};
>+
>+} // namespace WebCore
>+
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObserverCallback.idl b/Source/WebCore/page/ResizeObserverCallback.idl
>new file mode 100644
>index 0000000000..6fc9039235
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserverCallback.idl
>@@ -0,0 +1,30 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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.
>+ */
>+
>+// https://wicg.github.io/ResizeObserver/
>+
>+[
>+    Conditional=RESIZE_OBSERVER
>+] callback ResizeObserverCallback = void (sequence<ResizeObserverEntry> entries, ResizeObserver observer);
>diff --git a/Source/WebCore/page/ResizeObserverEntry.h b/Source/WebCore/page/ResizeObserverEntry.h
>new file mode 100644
>index 0000000000..bd6041ce62
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserverEntry.h
>@@ -0,0 +1,62 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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
>+
>+#if ENABLE(RESIZE_OBSERVER)
>+
>+#include "DOMRectReadOnly.h"
>+#include "Element.h"
>+#include "FloatRect.h"
>+#include <wtf/RefCounted.h>
>+
>+namespace WebCore {
>+
>+class Element;
>+
>+class ResizeObserverEntry : public RefCounted<ResizeObserverEntry> {
>+    WTF_MAKE_FAST_ALLOCATED;
>+public:
>+    static Ref<ResizeObserverEntry> create(Element* target, const FloatRect& contentRect)
>+    {
>+        return WTF::adoptRef(*new ResizeObserverEntry(target, contentRect));
>+    }
>+
>+    Element* target() { return m_target.get(); }
>+    DOMRectReadOnly* contentRect() { return m_contentRect.get(); }
>+
>+private:
>+    ResizeObserverEntry(Element* target, const FloatRect& contentRect)
>+        : m_target(target)
>+    {
>+        m_contentRect = DOMRectReadOnly::create(contentRect.x(), contentRect.y(), contentRect.width(), contentRect.height());
>+    }
>+
>+    RefPtr<Element> m_target;
>+    RefPtr<DOMRectReadOnly> m_contentRect;
>+};
>+
>+} // namespace WebCore
>+#endif // ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/WebCore/page/ResizeObserverEntry.idl b/Source/WebCore/page/ResizeObserverEntry.idl
>new file mode 100644
>index 0000000000..b051bb57be
>--- /dev/null
>+++ b/Source/WebCore/page/ResizeObserverEntry.idl
>@@ -0,0 +1,35 @@
>+/*
>+ * Copyright (C) 2019 Igalia S.L.
>+ *
>+ * 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.
>+ */
>+
>+// https://wicg.github.io/ResizeObserver/
>+
>+[
>+    Conditional=RESIZE_OBSERVER,
>+    ImplementationLacksVTable,
>+    EnabledBySetting=ResizeObserver
>+] interface ResizeObserverEntry {
>+    readonly attribute Element target;
>+    readonly attribute DOMRectReadOnly contentRect;
>+};
>\ No newline at end of file
>diff --git a/Source/WebCore/page/Settings.yaml b/Source/WebCore/page/Settings.yaml
>index ca4c57c869..21f6058e53 100644
>--- a/Source/WebCore/page/Settings.yaml
>+++ b/Source/WebCore/page/Settings.yaml
>@@ -796,3 +796,7 @@ editableImagesEnabled:
> 
> adClickAttributionEnabled:
>   initial: false
>+
>+resizeObserverEnabled:
>+  initial: false
>+  conditional: RESIZE_OBSERVER
>diff --git a/Source/WebKit/Shared/WebPreferences.yaml b/Source/WebKit/Shared/WebPreferences.yaml
>index 9b0eacaa9b..146b856bbd 100644
>--- a/Source/WebKit/Shared/WebPreferences.yaml
>+++ b/Source/WebKit/Shared/WebPreferences.yaml
>@@ -1380,6 +1380,14 @@ ProcessSwapOnCrossSiteNavigationEnabled:
>   category: experimental
>   webcoreBinding: none
> 
>+ResizeObserverEnabled:
>+  type: bool
>+  defaultValue: false
>+  humanReadableName: "Resize Observer"
>+  humanReadableDescription: "Enable Resize Observer support"
>+  category: experimental
>+  condition: ENABLE(RESIZE_OBSERVER)
>+
> # For internal features:
> # The type should be boolean.
> # You must provide a humanReadableName and humanReadableDescription for all debug features. They
>@@ -1551,3 +1559,11 @@ AdClickAttributionEnabled:
>   humanReadableDescription: "Enable Ad Click Attribution for Cross-Site Link Navigations"
>   webcoreBinding: RuntimeEnabledFeatures
>   category: internal
>+
>+ResizeObserverEnabled:
>+  type: bool
>+  defaultValue: true
>+  humanReadableName: "Resize Observer"
>+  humanReadableDescription: "Enable Resize Observer support"
>+  category: experimental
>+  condition: ENABLE(RESIZE_OBSERVER)
>diff --git a/Source/cmake/WebKitFeatures.cmake b/Source/cmake/WebKitFeatures.cmake
>index f70b817312..ce2bc9e108 100644
>--- a/Source/cmake/WebKitFeatures.cmake
>+++ b/Source/cmake/WebKitFeatures.cmake
>@@ -183,6 +183,7 @@ macro(WEBKIT_OPTION_BEGIN)
>     WEBKIT_OPTION_DEFINE(ENABLE_PUBLIC_SUFFIX_LIST "Toggle public suffix list support" PRIVATE ON)
>     WEBKIT_OPTION_DEFINE(ENABLE_QUOTA "Toggle Quota support" PRIVATE OFF)
>     WEBKIT_OPTION_DEFINE(ENABLE_REMOTE_INSPECTOR "Toggle remote inspector support" PRIVATE ON)
>+    WEBKIT_OPTION_DEFINE(ENABLE_RESIZE_OBSERVER "Enable Resize Observer support" PRIVATE ON)
>     WEBKIT_OPTION_DEFINE(ENABLE_RESOLUTION_MEDIA_QUERY "Toggle resolution media query support" PRIVATE OFF)
>     WEBKIT_OPTION_DEFINE(ENABLE_RESOURCE_LOAD_STATISTICS "Toggle resource load statistics support" PRIVATE OFF)
>     WEBKIT_OPTION_DEFINE(ENABLE_RESOURCE_USAGE "Toggle resource usage support" PRIVATE OFF)
>diff --git a/Tools/DumpRenderTree/TestOptions.cpp b/Tools/DumpRenderTree/TestOptions.cpp
>index c926612b1b..8215417a92 100644
>--- a/Tools/DumpRenderTree/TestOptions.cpp
>+++ b/Tools/DumpRenderTree/TestOptions.cpp
>@@ -111,6 +111,8 @@ TestOptions::TestOptions(const std::string& pathOrURL, const std::string& absolu
>             enableCSSLogical = parseBooleanTestHeaderValue(value);
>         else if (key == "internal:AdClickAttributionEnabled")
>             adClickAttributionEnabled = parseBooleanTestHeaderValue(value);
>+        else if (key == "enableResizeObserver")
>+            enableResizeObserver = parseBooleanTestHeaderValue(value);
>         pairStart = pairEnd + 1;
>     }
> }
>diff --git a/Tools/DumpRenderTree/TestOptions.h b/Tools/DumpRenderTree/TestOptions.h
>index c27e842a48..d885edbdeb 100644
>--- a/Tools/DumpRenderTree/TestOptions.h
>+++ b/Tools/DumpRenderTree/TestOptions.h
>@@ -46,6 +46,7 @@ struct TestOptions {
>     bool enableWebGPU { false };
>     bool enableCSSLogical { false };
>     bool adClickAttributionEnabled { false };
>+    bool enableResizeObserver { false };
>     std::string jscOptions;
> 
>     TestOptions(const std::string& pathOrURL, const std::string& absolutePath);
>diff --git a/Tools/DumpRenderTree/mac/DumpRenderTree.mm b/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>index d3f58c77d2..e66c05f3fd 100644
>--- a/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>+++ b/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>@@ -1012,6 +1012,7 @@ static void setWebPreferencesForTestOptions(const TestOptions& options)
>     preferences.webGPUEnabled = options.enableWebGPU;
>     preferences.CSSLogicalEnabled = options.enableCSSLogical;
>     preferences.adClickAttributionEnabled = options.adClickAttributionEnabled;
>+    preferences.resizeObserverEnabled = options.enableResizeObserver;
> }
> 
> // Called once on DumpRenderTree startup.

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