cc: Simplify task and its derived classes.

cc/tiles/tile.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_TILES_TILE_H_
 #define CC_TILES_TILE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 126 matching lines @@
   Id id_;
 
   // The rect bounding the changes in this Tile vs the previous tile it
   // replaced.
   gfx::Rect invalidated_content_rect_;
   // The |id_| of the Tile that was invalidated and replaced by this tile.
   Id invalidated_id_;
 
   unsigned scheduled_priority_;
 
-  scoped_refptr<RasterTask> raster_task_;
+  scoped_refptr<Task> raster_task_;
 
   DISALLOW_COPY_AND_ASSIGN(Tile);
 };
 
 using ScopedTilePtr = scoped_ptr<Tile, Tile::Deleter>;
 
 }  // namespace cc
 
 #endif  // CC_TILES_TILE_H_