cc: Simplify task and its derived classes.

cc/tiles/image_decode_controller.h

Index: cc/tiles/image_decode_controller.h
diff --git a/cc/tiles/image_decode_controller.h b/cc/tiles/image_decode_controller.h
index 4bf03d86bd8d41a84d4265c348c46c1497b59f0b..e0a8a4260f2d5535ee775325199780999bab218f 100644
--- a/cc/tiles/image_decode_controller.h
+++ b/cc/tiles/image_decode_controller.h
@@ -11,7 +11,7 @@
 
 namespace cc {
 
-class ImageDecodeTask;
+class DependencyTask;
 
 // ImageDecodeController is responsible for generating decode tasks, decoding
 // images, storing images in cache, and being able to return the decoded images
@@ -43,7 +43,7 @@ class CC_EXPORT ImageDecodeController {
   // a raster task.
   virtual bool GetTaskForImageAndRef(const DrawImage& image,
                                      uint64_t prepare_tiles_id,
-                                     scoped_refptr<ImageDecodeTask>* task) = 0;
+                                     scoped_refptr<DependencyTask>* task) = 0;
   // Unrefs an image. When the tile is finished, this should be called for every
   // GetTaskForImageAndRef call that returned true.
   virtual void UnrefImage(const DrawImage& image) = 0;