Efficiently handle image layer scaling

cc/picture_layer_impl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_PICTURE_LAYER_IMPL_H_
 #define CC_PICTURE_LAYER_IMPL_H_
 
 #include "cc/layer_impl.h"
 #include "cc/picture_layer_tiling.h"
 #include "cc/picture_layer_tiling_set.h"
@@ skipping 58 matching lines @@
   virtual bool areVisibleResourcesReady() const OVERRIDE;
 
   virtual scoped_ptr<base::Value> AsValue() const OVERRIDE;
 
 protected:
   PictureLayerImpl(LayerTreeImpl* treeImpl, int id);
   PictureLayerTiling* AddTiling(float contents_scale);
   void RemoveTiling(float contents_scale);
   void SyncFromActiveLayer(const PictureLayerImpl* other);
   void ManageTilings(bool animating_transform_to_screen);
+  virtual void CalculateRasterContentsScale(
+      bool animating_transform_to_screen,
+      float* raster_contents_scale,
+      float* low_res_raster_contents_scale);
   void CleanUpTilingsOnActiveLayer(
       std::vector<PictureLayerTiling*> used_tilings);
   PictureLayerImpl* PendingTwin() const;
   PictureLayerImpl* ActiveTwin() const;
 
   virtual void getDebugBorderProperties(
       SkColor* color, float* width) const OVERRIDE;
 
   scoped_ptr<PictureLayerTilingSet> tilings_;
   scoped_refptr<PicturePileImpl> pile_;
@@ skipping 15 matching lines @@
   float raster_source_scale_;
   bool raster_source_scale_was_animating_;
 
   friend class PictureLayer;
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };
 
 }
 
 #endif  // CC_PICTURE_LAYER_IMPL_H_