Layout test media/picture-in-picture-interruption.html is timing out for GTK since it was added in r233360 "Returning PiP'd video to fullscreen while playing leaves video muted."

--- /home/slave/webkitgtk/gtk-linux-64-release-tests/build/layout-test-results/media/picture-in-picture-interruption-expected.txt
+++ /home/slave/webkitgtk/gtk-linux-64-release-tests/build/layout-test-results/media/picture-in-picture-interruption-actual.txt
@@ -1,14 +1,3 @@
-This tests that video is in the correct media session state after ending a background interruption while pipped.
+CONSOLE MESSAGE: line 18: TypeError: video.webkitSetPresentationMode is not a function. (In 'video.webkitSetPresentationMode('picture-in-picture')', 'video.webkitSetPresentationMode' is undefined)
+FAIL: Timed out waiting for notifyDone to be called
 
-RUN(internals.settings.setAllowsPictureInPictureMediaPlayback(true))
-RUN(video.src = findMediaFile("video", "content/test"))
-EVENT(canplaythrough)
-RUN(video.play())
-EVENT(playing)
-EVENT(webkitpresentationmodechanged)
-RUN(internals.beginMediaSessionInterruption("enteringbackground"))
-EXPECTED (internals.mediaSessionState(video) == 'Playing') OK
-RUN(internals.endMediaSessionInterruption("enteringbackground"))
-EXPECTED (internals.mediaSessionState(video) == 'Playing') OK
-END OF TEST
-