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

Source/WebCore/rendering/RenderLayerCompositor.h

Index: Source/WebCore/rendering/RenderLayerCompositor.h
===================================================================
--- Source/WebCore/rendering/RenderLayerCompositor.h	(revision 115913)
+++ Source/WebCore/rendering/RenderLayerCompositor.h	(working copy)
@@ -135,9 +135,6 @@
     // Repaint parts of all composited layers that intersect the given absolute rectangle.
     void repaintCompositedLayersAbsoluteRect(const IntRect&);
 
-    // Returns true if the given layer needs it own backing store.
-    bool requiresOwnBackingStore(const RenderLayer*, const RenderLayer* compositingAncestorLayer) const;
-
     RenderLayer* rootRenderLayer() const;
     GraphicsLayer* rootGraphicsLayer() const;
     GraphicsLayer* scrollLayer() const;