cc: Simplify task and its derived classes.

cc/tiles/gpu_image_decode_controller.cc

Index: cc/tiles/gpu_image_decode_controller.cc
diff --git a/cc/tiles/gpu_image_decode_controller.cc b/cc/tiles/gpu_image_decode_controller.cc
index da9bd207010071c937c8c6490c1d6511db1b7ab8..00aeb2622e0a55ca9f127b7a62b612543c476fb3 100644
--- a/cc/tiles/gpu_image_decode_controller.cc
+++ b/cc/tiles/gpu_image_decode_controller.cc
@@ -10,7 +10,7 @@
 
 namespace cc {
 
-class ImageDecodeTaskImpl : public ImageDecodeTask {
+class ImageDecodeTaskImpl : public Task {
  public:
   ImageDecodeTaskImpl(GpuImageDecodeController* controller,
                       const DrawImage& image,
@@ -21,6 +21,10 @@ class ImageDecodeTaskImpl : public ImageDecodeTask {
         source_prepare_tiles_id_(source_prepare_tiles_id) {}
 
   // Overridden from Task:
+  void ScheduleOnOriginThread() override {}
+  void CompleteOnOriginThread() override {
+    controller_->RemovePendingTaskForImage(image_);
+  }
   void RunOnWorkerThread() override {
     TRACE_EVENT2("cc", "ImageDecodeTaskImpl::RunOnWorkerThread", "mode", "gpu",
                  "source_prepare_tiles_id", source_prepare_tiles_id_);
@@ -29,12 +33,6 @@ class ImageDecodeTaskImpl : public ImageDecodeTask {
     controller_->DecodeImage(image_);
   }
 
-  // Overridden from TileTask:
-  void ScheduleOnOriginThread(TileTaskClient* client) override {}
-  void CompleteOnOriginThread(TileTaskClient* client) override {
-    controller_->RemovePendingTaskForImage(image_);
-  }
-
  protected:
   ~ImageDecodeTaskImpl() override {}
 
@@ -54,7 +52,7 @@ GpuImageDecodeController::~GpuImageDecodeController() {}
 bool GpuImageDecodeController::GetTaskForImageAndRef(
     const DrawImage& image,
     uint64_t prepare_tiles_id,
-    scoped_refptr<ImageDecodeTask>* task) {
+    scoped_refptr<Task>* task) {
   auto image_id = image.image()->uniqueID();
   base::AutoLock lock(lock_);
   if (prerolled_images_.count(image_id) != 0) {
@@ -62,8 +60,7 @@ bool GpuImageDecodeController::GetTaskForImageAndRef(
     return false;
   }
 
-  scoped_refptr<ImageDecodeTask>& existing_task =
-      pending_image_tasks_[image_id];
+  scoped_refptr<Task>& existing_task = pending_image_tasks_[image_id];
   if (!existing_task) {
     existing_task = make_scoped_refptr(
         new ImageDecodeTaskImpl(this, image, prepare_tiles_id));