Refactor fixed layout mode

Source/core/rendering/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 154 matching lines @@
 
     static RenderLayerCompositor* frameContentsCompositor(RenderPart*);
     // Return true if the layers changed.
     static bool parentFrameContentLayers(RenderPart*);
 
     // Update the geometry of the layers used for clipping and scrolling in frames.
     void frameViewDidChangeLocation(const IntPoint& contentsOffset);
     void frameViewDidChangeSize();
     void frameViewDidScroll();
     void frameViewDidLayout();
+    void frameViewScrollbarsExistenceDidChange();
     void rootFixedBackgroundsChanged();
 
     bool scrollingLayerDidChange(RenderLayer*);
 
     String layerTreeAsText(LayerTreeFlags);
 
     virtual void didCommitChangesForLayer(const GraphicsLayer*) const OVERRIDE;
 
     GraphicsLayer* layerForHorizontalScrollbar() const { return m_layerForHorizontalScrollbar.get(); }
     GraphicsLayer* layerForVerticalScrollbar() const { return m_layerForVerticalScrollbar.get(); }
@@ skipping 175 matching lines @@
     int m_secondaryCompositedLayerCount; // count of layers that have to be composited because of stacking or overlap.
     double m_obligatoryBackingStoreBytes;
     double m_secondaryBackingStoreBytes;
 #endif
 };
 
 
 } // namespace WebCore
 
 #endif // RenderLayerCompositor_h