Simply rules for compositing fixed position elements

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 161 matching lines @@
 
     bool inOverlayFullscreenVideo() const { return m_inOverlayFullscreenVideo; }
 
 private:
     class OverlapMap;
 
 #if ENABLE(ASSERT)
     void assertNoUnresolvedDirtyBits();
 #endif
 
-    // Make updates to the layer based on viewport-constrained properties such as position:fixed. This can in turn affect
-    // compositing.
-    bool updateLayerIfViewportConstrained(RenderLayer*);
-
     // GraphicsLayerClient implementation
     virtual void notifyAnimationStarted(const GraphicsLayer*, double) OVERRIDE { }
     virtual void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect&) OVERRIDE;
 
     virtual bool isTrackingRepaints() const OVERRIDE;
 
     // Whether the given RL needs to paint into its own separate backing (and hence would need its own CompositedLayerMapping).
     bool needsOwnBacking(const RenderLayer*) const;
 
     void updateIfNeeded();
@@ skipping 61 matching lines @@
 #if USE(RUBBER_BANDING)
     OwnPtr<GraphicsLayer> m_layerForOverhangShadow;
 #endif
 
     bool m_inOverlayFullscreenVideo;
 };
 
 } // namespace blink
 
 #endif // RenderLayerCompositor_h