Add methods to RenderLayer to get at the painting or scrolling graphics layers, if present.

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 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 438 matching lines @@
 {
     // Project any rects for the current layer
     LayerHitTestRects::const_iterator layerIter = layerRects.find(curLayer);
     if (layerIter != layerRects.end()) {
         // Find the enclosing composited layer when it's in another document (for non-composited iframes).
         const RenderLayer* compositedLayer = enclosingCompositedLayer(layerIter->key);
         if (!compositedLayer)
             return;
 
         // Find the appropriate GraphicsLayer for the composited RenderLayer.
-        GraphicsLayer* graphicsLayer;
-        if (compositedLayer->compositingState() == PaintsIntoGroupedBacking) {
-            graphicsLayer = compositedLayer->groupedMapping()->squashingLayer();
-        } else {
-            ASSERT(compositedLayer->hasCompositedLayerMapping());
-            CompositedLayerMappingPtr compositedLayerMapping = compositedLayer->compositedLayerMapping();
-            graphicsLayer = compositedLayerMapping->scrollingContentsLayer();
-            if (!graphicsLayer)
-                graphicsLayer = compositedLayerMapping->mainGraphicsLayer();
-        }
+        GraphicsLayer* graphicsLayer = compositedLayer->graphicsLayerBackingForScrolling();
 
         GraphicsLayerHitTestRects::iterator glIter = graphicsRects.find(graphicsLayer);
         Vector<LayoutRect>* glRects;
         if (glIter == graphicsRects.end())
             glRects = &graphicsRects.add(graphicsLayer, Vector<LayoutRect>()).storedValue->value;
         else
             glRects = &glIter->value;
 
         // Transform each rect to the co-ordinate space of the graphicsLayer.
         for (size_t i = 0; i < layerIter->value.size(); ++i) {
@@ skipping 512 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0)
         return blink::WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace WebCore