Revert 114283 - Avoid using backing store for compositing layers that just need to clip

Source/WebCore/rendering/RenderLayerBacking.h

 /*
  * Copyright (C) 2009, 2010, 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 78 matching lines @@
     GraphicsLayer* parentForSublayers() const { return m_clippingLayer ? m_clippingLayer.get() : m_graphicsLayer.get(); }
     GraphicsLayer* childForSuperlayers() const { return m_ancestorClippingLayer ? m_ancestorClippingLayer.get() : m_graphicsLayer.get(); }
 
     // RenderLayers with backing normally short-circuit paintLayer() because
     // their content is rendered via callbacks from GraphicsLayer. However, the document
     // layer is special, because it has a GraphicsLayer to act as a container for the GraphicsLayers
     // for descendants, but its contents usually render into the window (in which case this returns true).
     // This returns false for other layers, and when the document layer actually needs to paint into its backing store
     // for some reason.
     bool paintsIntoWindow() const;
-    
-    // Returns true for a composited layer that has no backing store of its own, so
-    // paints into some ancestor layer.
-    bool paintsIntoCompositedAncestor() const { return !m_requiresOwnBackingStore; }
-
-    void setRequiresOwnBackingStore(bool flag) { m_requiresOwnBackingStore = flag; }
 
     void setContentsNeedDisplay();
     // r is in the coordinate space of the layer's render object
     void setContentsNeedDisplayInRect(const IntRect&);
 
     // Notification from the renderer that its content changed.
     void contentChanged(ContentChangeType);
 
     // Interface to start, finish, suspend and resume animations and transitions
     bool startTransition(double, CSSPropertyID, const RenderStyle* fromStyle, const RenderStyle* toStyle);
@@ skipping 120 matching lines @@
 
     OwnPtr<GraphicsLayer> m_layerForHorizontalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForVerticalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForScrollCorner;
 
     IntRect m_compositedBounds;
 
     bool m_artificiallyInflatedBounds;      // bounds had to be made non-zero to make transform-origin work
     bool m_isMainFrameRenderViewLayer;
     bool m_usingTiledCacheLayer;
-    bool m_requiresOwnBackingStore;
 #if ENABLE(CSS_FILTERS)
     bool m_canCompositeFilters;
 #endif
 };
 
 } // namespace WebCore
 
 #endif // USE(ACCELERATED_COMPOSITING)
 
 #endif // RenderLayerBacking_h