Shifting layer position for sticky element to avoid passing unnessary variable to cc

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.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 352 matching lines @@
       const FloatSize& relative_compositing_bounds_size,
       const IntRect& clipping_box);
   void UpdateBackgroundLayerGeometry(
       const FloatSize& relative_compositing_bounds_size);
   void UpdateDecorationOutlineLayerGeometry(
       const FloatSize& relative_compositing_bounds_size);
   void UpdateScrollingLayerGeometry(const IntRect& local_compositing_bounds);
   void UpdateChildClippingMaskLayerGeometry();
   void UpdateStickyConstraints(const ComputedStyle&);
 
+  bool UsesCompositedStickyPosition() const;

[flackr, 2017/06/09 17:33:33]

Add a comment. This function is determining whether the compositor will be
responsible for applying the sticky position offset for this composited layer.

[yigu, 2017/06/09 17:41:16]

Done.

+
   void CreatePrimaryGraphicsLayer();
   void DestroyGraphicsLayers();
 
   std::unique_ptr<GraphicsLayer> CreateGraphicsLayer(
       CompositingReasons,
       SquashingDisallowedReasons = kSquashingDisallowedReasonsNone);
   bool ToggleScrollbarLayerIfNeeded(std::unique_ptr<GraphicsLayer>&,
                                     bool needs_layer,
                                     CompositingReasons);
 
@@ skipping 324 matching lines @@
   unsigned background_paints_onto_graphics_layer_ : 1;
 
   bool draws_background_onto_content_layer_;
 
   friend class CompositedLayerMappingTest;
 };
 
 }  // namespace blink
 
 #endif  // CompositedLayerMapping_h