cc: Generate tilings at other scales for impl-side painting

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 32 matching lines @@
   // PushPropertiesTo active tree => pending tree
   void SyncFromActiveLayer();
   void SyncTiling(const PictureLayerTiling* tiling);
 
   // Mask-related functions
   void SetIsMask(bool is_mask);
   virtual ResourceProvider::ResourceId contentsResourceId() const OVERRIDE;
 
 protected:
   PictureLayerImpl(LayerTreeImpl* treeImpl, int id);
-  void AddTiling(float contents_scale, gfx::Size tile_size);
+  PictureLayerTiling* AddTiling(float contents_scale);
   void SyncFromActiveLayer(const PictureLayerImpl* other);
   gfx::Size TileSize() const;
   void ManageTilings(float ideal_contents_scale);
+  void CleanUpUnusedTilings(std::vector<PictureLayerTiling*> used_tilings);
 
   PictureLayerTilingSet tilings_;
   scoped_refptr<PicturePileImpl> pile_;
   Region invalidation_;
 
   gfx::Transform last_screen_space_transform_;
   double last_update_time_;
   gfx::Size last_bounds_;
   gfx::Size last_content_bounds_;
-  float last_content_scale_x_;
-  float last_content_scale_y_;
+  float last_content_scale_;
+  float ideal_contents_scale_;
   bool is_mask_;
 
   friend class PictureLayer;
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };
 
 }
 
 #endif  // CC_PICTURE_LAYER_IMPL_H_