cc: Use maximum tiling contents scales for picture layer scale

cc/picture_layer_tiling_set.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_TILING_SET_H_
 #define CC_PICTURE_LAYER_TILING_SET_H_
 
 #include "cc/picture_layer_tiling.h"
 #include "cc/region.h"
 #include "cc/scoped_ptr_vector.h"
@@ skipping 12 matching lines @@
      const Region& invalidation);
   void Clone(const PictureLayerTiling* tiling, const Region& invalidation);
 
   void SetLayerBounds(gfx::Size layer_bounds);
   gfx::Size LayerBounds() const;
 
   const PictureLayerTiling* AddTiling(
       float contents_scale,
       gfx::Size tile_size);
   size_t num_tilings() const { return tilings_.size(); }
+  PictureLayerTiling* tiling_at(size_t idx) { return tilings_[idx]; }
 
   void Reset();
 
   void UpdateTilePriorities(
       WhichTree tree,
       const gfx::Size& device_viewport,
       float layer_content_scale_x,
       float layer_content_scale_y,
       const gfx::Transform& last_screen_transform,
       const gfx::Transform& current_screen_transform,
@@ skipping 42 matching lines @@
   gfx::Size layer_bounds_;
   ScopedPtrVector<PictureLayerTiling> tilings_;
   Region invalidation_;
 
   friend class Iterator;
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_LAYER_TILING_SET_H_