Run CSSOM smooth scroll animations on the compositor when possible

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 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
@@ skipping 192 matching lines @@
 
     rootRenderLayer()->updateDescendantDependentFlagsForEntireSubtree();
     m_renderView.commitPendingSelection();
 
     lifecycle().advanceTo(DocumentLifecycle::InCompositingUpdate);
     updateIfNeeded();
     lifecycle().advanceTo(DocumentLifecycle::CompositingClean);
 
     DocumentAnimations::startPendingAnimations(m_renderView.document());
 
+    m_renderView.frameView()->updateCompositorScrollAnimations();
+    if (const FrameView::ScrollableAreaSet* animatingScrollableAreas = m_renderView.frameView()->animatingScrollableAreas()) {
+        for (ScrollableArea* scrollableArea : *animatingScrollableAreas)
+            scrollableArea->updateCompositorScrollAnimations();
+    }
+
 #if ENABLE(ASSERT)
     ASSERT(lifecycle().state() == DocumentLifecycle::CompositingClean);
     assertNoUnresolvedDirtyBits();
     for (Frame* child = m_renderView.frameView()->frame().tree().firstChild(); child; child = child->tree().nextSibling()) {
         if (child->isLocalFrame())
             toLocalFrame(child)->contentRenderer()->compositor()->assertNoUnresolvedDirtyBits();
     }
 #endif
 }
 
@@ skipping 950 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink