implement the logic to set tile priorities based on current matrix

cc/picture_layer_tiling.h

Index: cc/picture_layer_tiling.h
diff --git a/cc/picture_layer_tiling.h b/cc/picture_layer_tiling.h
index d1ccc8213afdae1988f8a51ce266077916c5c05e..b501bf4b85a78c8b6bbac3bc65529895e3b96bc9 100644
--- a/cc/picture_layer_tiling.h
+++ b/cc/picture_layer_tiling.h
@@ -86,6 +86,13 @@ class CC_EXPORT PictureLayerTiling {
 
   void Reset() { return tiles_.clear(); }
 
+  void UpdateTilePriorities(const gfx::Size& device_view_port,
+                            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);
+
  protected:
   typedef std::pair<int, int> TileMapKey;
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;