cc: Simplify the logic for deciding to update tile priorities.

cc/resources/picture_layer_tiling.h

Index: cc/resources/picture_layer_tiling.h
diff --git a/cc/resources/picture_layer_tiling.h b/cc/resources/picture_layer_tiling.h
index 2661249963a784f27328bee069e7d828cbd888db..f7af5f33202b968219e49f9a0bc105022e6eb4a6 100644
--- a/cc/resources/picture_layer_tiling.h
+++ b/cc/resources/picture_layer_tiling.h
@@ -138,7 +138,6 @@ class CC_EXPORT PictureLayerTiling {
       float current_layer_contents_scale,
       const gfx::Transform& last_screen_transform,
       const gfx::Transform& current_screen_transform,
-      int current_source_frame_number,
       double current_frame_time,
       bool store_screen_space_quads_on_tiles,
       size_t max_tiles_for_interest_area);
@@ -150,6 +149,10 @@ class CC_EXPORT PictureLayerTiling {
 
   scoped_ptr<base::Value> AsValue() const;
 
+  bool NeedsUpdateForFrameAtTime(double frame_time) {
+    return frame_time != last_impl_frame_time_;
+  }
+
  protected:
   typedef std::pair<int, int> TileMapKey;
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;