cc: Simplify task and its derived classes.

cc/tiles/tile_manager.h

Index: cc/tiles/tile_manager.h
diff --git a/cc/tiles/tile_manager.h b/cc/tiles/tile_manager.h
index 75f1b2dfd62b4ae488146ef52dcf8d42ba2a5f44..4cda7f9c942d3ed42641a5862136d5cd4f467880 100644
--- a/cc/tiles/tile_manager.h
+++ b/cc/tiles/tile_manager.h
@@ -248,7 +248,7 @@ class CC_EXPORT TileManager {
 
   void FreeResourcesForTile(Tile* tile);
   void FreeResourcesForTileAndNotifyClientIfTileWasReadyToDraw(Tile* tile);
-  scoped_refptr<RasterTask> CreateRasterTask(
+  scoped_refptr<DependencyTask> CreateRasterTask(
       const PrioritizedTile& prioritized_tile);
 
   scoped_ptr<EvictionTilePriorityQueue>
@@ -275,7 +275,7 @@ class CC_EXPORT TileManager {
   void DidFinishRunningTileTasksRequiredForDraw();
   void DidFinishRunningAllTileTasks();
 
-  scoped_refptr<TileTask> CreateTaskSetFinishedTask(
+  scoped_refptr<DependencyTask> CreateTaskSetFinishedTask(
       void (TileManager::*callback)());
 
   scoped_ptr<base::trace_event::ConvertableToTraceFormat>
@@ -305,12 +305,12 @@ class CC_EXPORT TileManager {
 
   std::vector<Tile*> released_tiles_;
 
-  std::vector<scoped_refptr<TileTask>> orphan_tasks_;
+  std::vector<scoped_refptr<DependencyTask>> orphan_tasks_;
 
   TaskGraph graph_;
-  scoped_refptr<TileTask> required_for_activation_done_task_;
-  scoped_refptr<TileTask> required_for_draw_done_task_;
-  scoped_refptr<TileTask> all_done_task_;
+  scoped_refptr<DependencyTask> required_for_activation_done_task_;
+  scoped_refptr<DependencyTask> required_for_draw_done_task_;
+  scoped_refptr<DependencyTask> all_done_task_;
 
   UniqueNotifier more_tiles_need_prepare_check_notifier_;