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

Source/WebCore/rendering/RenderLayerBacking.h

Index: Source/WebCore/rendering/RenderLayerBacking.h
===================================================================
--- Source/WebCore/rendering/RenderLayerBacking.h	(revision 115913)
+++ Source/WebCore/rendering/RenderLayerBacking.h	(working copy)
@@ -96,13 +96,7 @@
     // 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&);
@@ -242,7 +236,6 @@
     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