Fix & clarify some comments in compositing. Rename clippedByAncestor to more accurately

Source/core/rendering/compositing/RenderLayerCompositor.h

 /*
  * Copyright (C) 2009 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 96 matching lines @@
 
     enum UpdateLayerCompositingStateOptions {
         Normal,
         UseChickenEggHacks, // Use this to trigger temporary chicken-egg hacks. See crbug.com/339892.
     };
 
     // Update the compositing dirty bits, based on the compositing-impacting properties of the layer.
     // (At the moment, it also has some legacy compatibility hacks.)
     void updateLayerCompositingState(RenderLayer*, UpdateLayerCompositingStateOptions = Normal);
 
-    // Whether layer's compositedLayerMapping needs a GraphicsLayer to do clipping by an ancestor (non-stacking-context parent with overflow).
-    bool clippedByAncestor(const RenderLayer*) const;
+    // Returns whether this layer is clipped by another layer that is not an ancestor of the given layer in the stacking context hierarchy.
+    bool clippedByNonAncestorInStackingTree(const RenderLayer*) const;
     // Whether layer's compositedLayerMapping needs a GraphicsLayer to clip z-order children of the given RenderLayer.
     bool clipsCompositingDescendants(const RenderLayer*) const;
 
     // Whether the given layer needs an extra 'contents' layer.
     bool needsContentsCompositingLayer(const RenderLayer*) const;
 
     bool supportsFixedRootBackgroundCompositing() const;
     bool needsFixedRootBackgroundLayer(const RenderLayer*) const;
     GraphicsLayer* fixedRootBackgroundLayer() const;
     void setNeedsUpdateFixedBackground() { m_needsUpdateFixedBackground = true; }
@@ skipping 227 matching lines @@
     OwnPtr<GraphicsLayer> m_layerForVerticalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForScrollCorner;
 #if USE(RUBBER_BANDING)
     OwnPtr<GraphicsLayer> m_layerForOverhangShadow;
 #endif
 };
 
 } // namespace WebCore
 
 #endif // RenderLayerCompositor_h