cc: Simplify task and its derived classes.

cc/tiles/software_image_decode_controller.cc

Index: cc/tiles/software_image_decode_controller.cc
diff --git a/cc/tiles/software_image_decode_controller.cc b/cc/tiles/software_image_decode_controller.cc
index 93d017f186fa0dd34000ca815ef3f7ff637cdc17..96f1697d1270276750888014a0f673dfaf59e781 100644
--- a/cc/tiles/software_image_decode_controller.cc
+++ b/cc/tiles/software_image_decode_controller.cc
@@ -36,7 +36,7 @@ class AutoRemoveKeyFromTaskMap {
  public:
   AutoRemoveKeyFromTaskMap(
       std::unordered_map<SoftwareImageDecodeController::ImageKey,
-                         scoped_refptr<ImageDecodeTask>,
+                         scoped_refptr<Task>,
                          SoftwareImageDecodeController::ImageKeyHash>* task_map,
       const SoftwareImageDecodeController::ImageKey& key)
       : task_map_(task_map), key_(key) {}
@@ -44,12 +44,12 @@ class AutoRemoveKeyFromTaskMap {
 
  private:
   std::unordered_map<SoftwareImageDecodeController::ImageKey,
-                     scoped_refptr<ImageDecodeTask>,
+                     scoped_refptr<Task>,
                      SoftwareImageDecodeController::ImageKeyHash>* task_map_;
   SoftwareImageDecodeController::ImageKey key_;
 };
 
-class ImageDecodeTaskImpl : public ImageDecodeTask {
+class ImageDecodeTaskImpl : public Task {
  public:
   ImageDecodeTaskImpl(SoftwareImageDecodeController* controller,
                       const SoftwareImageDecodeController::ImageKey& image_key,
@@ -62,6 +62,10 @@ class ImageDecodeTaskImpl : public ImageDecodeTask {
         source_prepare_tiles_id_(source_prepare_tiles_id) {}
 
   // Overridden from Task:
+  void ScheduleOnOriginThread() override {}
+  void CompleteOnOriginThread() override {
+    controller_->RemovePendingTask(image_key_);
+  }
   void RunOnWorkerThread() override {
     TRACE_EVENT2("cc", "ImageDecodeTaskImpl::RunOnWorkerThread", "mode",
                  "software", "source_prepare_tiles_id",
@@ -71,12 +75,6 @@ class ImageDecodeTaskImpl : public ImageDecodeTask {
     controller_->DecodeImage(image_key_, image_);
   }
 
-  // Overridden from TileTask:
-  void ScheduleOnOriginThread(TileTaskClient* client) override {}
-  void CompleteOnOriginThread(TileTaskClient* client) override {
-    controller_->RemovePendingTask(image_key_);
-  }
-
  protected:
   ~ImageDecodeTaskImpl() override {}
 
@@ -157,7 +155,7 @@ SoftwareImageDecodeController::~SoftwareImageDecodeController() {
 bool SoftwareImageDecodeController::GetTaskForImageAndRef(
     const DrawImage& image,
     uint64_t prepare_tiles_id,
-    scoped_refptr<ImageDecodeTask>* task) {
+    scoped_refptr<Task>* task) {
   // If the image already exists or if we're going to create a task for it, then
   // we'll likely need to ref this image (the exception is if we're prerolling
   // the image only). That means the image is or will be in the cache. When the
@@ -184,7 +182,7 @@ bool SoftwareImageDecodeController::GetTaskForImageAndRef(
   if (!CanHandleImage(key)) {
     base::AutoLock lock(lock_);
     if (prerolled_images_.count(key.image_id()) == 0) {
-      scoped_refptr<ImageDecodeTask>& existing_task = pending_image_tasks_[key];
+      scoped_refptr<Task>& existing_task = pending_image_tasks_[key];
       if (!existing_task) {
         existing_task = make_scoped_refptr(
             new ImageDecodeTaskImpl(this, key, image, prepare_tiles_id));
@@ -217,7 +215,7 @@ bool SoftwareImageDecodeController::GetTaskForImageAndRef(
   }
 
   // If the task exists, return it.
-  scoped_refptr<ImageDecodeTask>& existing_task = pending_image_tasks_[key];
+  scoped_refptr<Task>& existing_task = pending_image_tasks_[key];
   if (existing_task) {
     RefImage(key);
     *task = existing_task;