cc: Simplify task and its derived classes.

cc/tiles/gpu_image_decode_controller.h

 // Copyright 2016 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_GPU_IMAGE_DECODE_CONTROLLER_H_
 #define CC_TILES_GPU_IMAGE_DECODE_CONTROLLER_H_
 
 #include <unordered_map>
 #include <unordered_set>
 
 #include "base/synchronization/lock.h"
 #include "cc/base/cc_export.h"
 #include "cc/tiles/image_decode_controller.h"
 
 namespace cc {
 
 class CC_EXPORT GpuImageDecodeController : public ImageDecodeController {
  public:
   GpuImageDecodeController();
   ~GpuImageDecodeController() override;
 
   // ImageDecodeController overrides.
   bool GetTaskForImageAndRef(const DrawImage& image,
                              uint64_t prepare_tiles_id,
-                             scoped_refptr<ImageDecodeTask>* task) override;
+                             scoped_refptr<Task>* task) override;
   void UnrefImage(const DrawImage& image) override;
   DecodedDrawImage GetDecodedImageForDraw(const DrawImage& draw_image) override;
   void DrawWithImageFinished(const DrawImage& image,
                              const DecodedDrawImage& decoded_image) override;
   void ReduceCacheUsage() override;
 
   void DecodeImage(const DrawImage& image);
 
   void RemovePendingTaskForImage(const DrawImage& image);
 
  private:
   base::Lock lock_;
 
   std::unordered_set<uint32_t> prerolled_images_;
-  std::unordered_map<uint32_t, scoped_refptr<ImageDecodeTask>>
-      pending_image_tasks_;
+  std::unordered_map<uint32_t, scoped_refptr<Task>> pending_image_tasks_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_GPU_IMAGE_DECODE_CONTROLLER_H_