Disable scrolling for fullscreen elements by changing scroll layer size.

After https://codereview.chromium.org/476113004 CC depends on the
tree structure of scroll/clip layers to determine the viewport size, so
detaching them breaks fullscreen mode.  Switch to the other
approach of changing the scroll layer bounds.

BUG=410452

Review URL: https://codereview.chromium.org/558813003

git-svn-id: svn://svn.chromium.org/blink/trunk@181926 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

@@ -158,14 +158,13 @@ void ScrollingCoordinator::updateAfterCompositingChangeIfNeeded()
     // The mainFrame view doesn't get included in the FrameTree below, so we
     // update its size separately.
     if (WebLayer* scrollingWebLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0) {
-        scrollingWebLayer->setBounds(frameView->contentsSize());
-        // If there is a fullscreen element, set the scroll clip layer to 0 so main frame won't scroll.
+        // If there is a fullscreen element, set the scroll bounds to empty so the main frame won't scroll.
         Document* mainFrameDocument = m_page->deprecatedLocalMainFrame()->document();
         Element* fullscreenElement = Fullscreen::fullscreenElementFrom(*mainFrameDocument);
         if (fullscreenElement && fullscreenElement != mainFrameDocument->documentElement())
-            scrollingWebLayer->setScrollClipLayer(0);
+            scrollingWebLayer->setBounds(IntSize());
         else
-            scrollingWebLayer->setScrollClipLayer(toWebLayer(frameView->layerForContainer()));
+            scrollingWebLayer->setBounds(frameView->contentsSize());
     }
 
     const FrameTree& tree = m_page->mainFrame()->tree();

third_party/WebKit/Source/web/tests/WebFrameTest.cpp

@@ -5748,17 +5748,17 @@ TEST_F(WebFrameTest, FullscreenLayerNonScrollable)
     webViewImpl->didEnterFullScreen();
     webViewImpl->layout();
 
-    // Verify that the main frame is not scrollable.
+    // Verify that the main frame bounds are empty.
     ASSERT_TRUE(Fullscreen::isFullScreen(*document));
     WebLayer* webScrollLayer = webViewImpl->compositor()->scrollLayer()->platformLayer();
-    ASSERT_FALSE(webScrollLayer->scrollable());
+    ASSERT_EQ(WebSize(), webScrollLayer->bounds());
 
     // Verify that the main frame is scrollable upon exiting fullscreen.
     webViewImpl->didExitFullScreen();
     webViewImpl->layout();
     ASSERT_FALSE(Fullscreen::isFullScreen(*document));
     webScrollLayer = webViewImpl->compositor()->scrollLayer()->platformLayer();
-    ASSERT_TRUE(webScrollLayer->scrollable());
+    ASSERT_NE(WebSize(), webScrollLayer->bounds());
 }
 
 TEST_F(WebFrameTest, FullscreenMainFrameScrollable)