cc: Only create tilings for layers that draws content.

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 10 matching lines @@
   void CloneFrom(const PictureLayerTilingSet& other);
 
   void SetLayerBounds(gfx::Size layer_bounds);
   gfx::Size LayerBounds() const;
 
   void Invalidate(const Region& invalidation);
 
   void AddTiling(float contents_scale, gfx::Size tile_size);
   size_t num_tilings() const { return tilings_.size(); }
 
+  void Reset();
+
   void UpdateTilePriorities(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,
                             double time_delta);
 
   // For a given rect, iterates through tiles that can fill it.  If no
   // set of tiles with resources can fill the rect, then it will iterate
   // through null tiles with valid geometry_rect() until the rect is full.
@@ skipping 33 matching lines @@
   PictureLayerTilingClient* client_;
   gfx::Size layer_bounds_;
   ScopedPtrVector<PictureLayerTiling> tilings_;
 
   friend class Iterator;
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_LAYER_TILING_SET_H_