Make composited scrolling codepaths co-operate.

Source/core/rendering/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 321 matching lines @@
     if (!m_needsUpdateCompositingRequirementsState)
         return;
 
     TRACE_EVENT0("blink_rendering,comp-scroll", "RenderLayerCompositor::updateCompositingRequirementsState");
 
     m_needsUpdateCompositingRequirementsState = false;
 
     if (!rootRenderLayer() || !rootRenderLayer()->acceleratedCompositingForOverflowScrollEnabled())
         return;
 
-    const bool compositorDrivenAcceleratedScrollingEnabled = rootRenderLayer()->compositorDrivenAcceleratedScrollingEnabled();
-
-    const FrameView::ScrollableAreaSet* scrollableAreas = m_renderView->frameView()->scrollableAreas();
-    if (!compositorDrivenAcceleratedScrollingEnabled && !scrollableAreas)
-        return;
-
     for (HashSet<RenderLayer*>::iterator it = m_outOfFlowPositionedLayers.begin(); it != m_outOfFlowPositionedLayers.end(); ++it)
         (*it)->updateHasUnclippedDescendant();
 
-    if (!compositorDrivenAcceleratedScrollingEnabled) {
-        for (FrameView::ScrollableAreaSet::iterator it = scrollableAreas->begin(); it != scrollableAreas->end(); ++it)
-            (*it)->updateNeedsCompositedScrolling();
-    }
+    const FrameView::ScrollableAreaSet* scrollableAreas = m_renderView->frameView()->scrollableAreas();
+    if (!scrollableAreas)
+        return;
+
+    for (FrameView::ScrollableAreaSet::iterator it = scrollableAreas->begin(); it != scrollableAreas->end(); ++it)
+        (*it)->updateNeedsCompositedScrolling();
 }
 
 static RenderVideo* findFullscreenVideoRenderer(Document* document)
 {
     Element* fullscreenElement = FullscreenElementStack::currentFullScreenElementFrom(document);
     while (fullscreenElement && fullscreenElement->isFrameOwnerElement()) {
         document = toHTMLFrameOwnerElement(fullscreenElement)->contentDocument();
         if (!document)
             return 0;
         fullscreenElement = FullscreenElementStack::currentFullScreenElementFrom(document);
@@ skipping 2419 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore