cc: Block drawing of tiles without twins.

cc/resources/picture_layer_tiling.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_RESOURCES_PICTURE_LAYER_TILING_H_
 #define CC_RESOURCES_PICTURE_LAYER_TILING_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 264 matching lines @@
   gfx::Rect ExpandRectEquallyToAreaBoundedBy(
       const gfx::Rect& starting_rect,
       int64 target_area,
       const gfx::Rect& bounding_rect,
       RectExpansionCache* cache);
 
   bool has_ever_been_updated() const {
     return last_impl_frame_time_in_seconds_ != 0.0;
   }
 
+  int tiles_size() const;
+
  protected:
   friend class CoverageIterator;
   friend class TilingRasterTileIterator;
   friend class TilingEvictionTileIterator;
 
   typedef std::pair<int, int> TileMapKey;
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;
 
   PictureLayerTiling(float contents_scale,
                      const gfx::Size& layer_bounds,
@@ skipping 59 matching lines @@
 
  private:
   DISALLOW_ASSIGN(PictureLayerTiling);
 
   RectExpansionCache expansion_cache_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_LAYER_TILING_H_