cc: Speed up CleanUpImageDecodeTasks a bit.

cc/resources/tile_manager.h

Index: cc/resources/tile_manager.h
diff --git a/cc/resources/tile_manager.h b/cc/resources/tile_manager.h
index 1e5d7ff1cd5dbce91bfaceabc961b4a1500bcb66..095f80fc6691f5c1e27618ceff25a5e3c42047a1 100644
--- a/cc/resources/tile_manager.h
+++ b/cc/resources/tile_manager.h
@@ -93,6 +93,9 @@ class CC_EXPORT TileManager : public RasterWorkerPoolClient {
       ++resources_releasable_;
     }
   }
+  RasterWorkerPool* RasterWorkerPoolForTesting() {
+    return raster_worker_pool_.get();
+  }
 
  protected:
   TileManager(TileManagerClient* client,
@@ -176,6 +179,9 @@ class CC_EXPORT TileManager : public RasterWorkerPoolClient {
   typedef base::hash_map<int, PixelRefTaskMap> LayerPixelRefTaskMap;
   LayerPixelRefTaskMap image_decode_tasks_;
 
+  typedef base::hash_map<int, int> LayerCountMap;
+  LayerCountMap used_layer_counts_;
+
   RasterTaskCompletionStats update_visible_tiles_stats_;
 
   DISALLOW_COPY_AND_ASSIGN(TileManager);