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

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 132 matching lines @@
       bool store_screen_space_quads_on_tiles,
       size_t max_tiles_for_interest_area);
 
   // Copies the src_tree priority into the dst_tree priority for all tiles.
   // The src_tree priority is reset to the lowest priority possible.  This
   // also updates the pile on each tile to be the current client's pile.
   void DidBecomeActive();
 
   scoped_ptr<base::Value> AsValue() const;
 
+  bool needs_first_time_update_tile_priorities() const {
+    return last_impl_frame_time_ == 0.0;
+  }
+
  protected:
   typedef std::pair<int, int> TileMapKey;
   typedef base::hash_map<TileMapKey, scoped_refptr<Tile> > TileMap;
 
   explicit PictureLayerTiling(float contents_scale);
   Tile* TileAt(int, int) const;
   void CreateTilesFromContentRect(gfx::Rect layer_rect);
   void CreateTile(int i, int j);
 
   PictureLayerTilingClient* client_;
   float contents_scale_;
   gfx::Size layer_bounds_;
   gfx::Rect last_prioritized_rect_;
   // It is not legal to have a NULL tile in the tiles_ map.
   TileMap tiles_;
   TilingData tiling_data_;
   TileResolution resolution_;
   int last_source_frame_number_;
   double last_impl_frame_time_;
 
   friend class CoverageIterator;
 
  private:
   DISALLOW_ASSIGN(PictureLayerTiling);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_LAYER_TILING_H_