notifications: Use standard task-runners to run image loader callbacks.

Instead of using the id of the worker-thread to keep track of the thread to
run the image-loader callbacks on, use the task-runner of the thread instead.

BUG=none
R=mkwst@chromium.org

Review URL: https://codereview.chromium.org/897733002

Cr-Commit-Position: refs/heads/master@{#315109}

content/child/notifications/notification_image_loader.cc

@@ -7,7 +7,6 @@
 #include "base/logging.h"
 #include "content/child/child_thread_impl.h"
 #include "content/child/image_decoder.h"
-#include "content/child/worker_task_runner.h"
 #include "third_party/WebKit/public/platform/Platform.h"
 #include "third_party/WebKit/public/platform/WebURL.h"
 #include "third_party/WebKit/public/platform/WebURLLoader.h"
@@ -27,12 +26,14 @@ NotificationImageLoader::NotificationImageLoader(
 
 NotificationImageLoader::~NotificationImageLoader() {}
 
-void NotificationImageLoader::StartOnMainThread(const WebURL& image_url,
-                                                int worker_thread_id) {
+void NotificationImageLoader::StartOnMainThread(
+    const WebURL& image_url,
+    const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner) {
   DCHECK(ChildThreadImpl::current());
   DCHECK(!url_loader_);
+  DCHECK(worker_task_runner);
 
-  worker_thread_id_ = worker_thread_id;
+  worker_task_runner_ = worker_task_runner;
 
   WebURLRequest request(image_url);
   request.setRequestContext(WebURLRequest::RequestContextImage);
@@ -79,14 +80,10 @@ void NotificationImageLoader::didFail(WebURLLoader* loader,
 
 void NotificationImageLoader::RunCallbackOnWorkerThread() {
   scoped_refptr<NotificationImageLoader> loader = make_scoped_refptr(this);
-  if (!worker_thread_id_) {
+  if (worker_task_runner_->BelongsToCurrentThread())
     callback_.Run(loader);
-    return;
-  }
-
-  WorkerTaskRunner::Instance()->PostTask(
-      worker_thread_id_,
-      base::Bind(callback_, loader));
+  else
+    worker_task_runner_->PostTask(FROM_HERE, base::Bind(callback_, loader));
 }
 
 }  // namespace content

content/child/notifications/notification_image_loader.h

@@ -14,6 +14,10 @@
 
 class SkBitmap;
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace blink {
 class WebURL;
 struct WebURLError;
@@ -41,9 +45,11 @@ class NotificationImageLoader
       const NotificationImageLoadedCallback& callback);
 
   // Asynchronously starts loading |image_url|.
-  // Must be called on the main thread. |worker_thread_id| identifies the id
-  // of the thread on which the callback should be executed upon completion.
-  void StartOnMainThread(const blink::WebURL& image_url, int worker_thread_id);
+  // Must be called on the main thread. The callback should be executed by
+  // |worker_task_runner|.
+  void StartOnMainThread(
+      const blink::WebURL& image_url,
+      const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner);
 
   // Returns the SkBitmap resulting from decoding the loaded buffer.
   SkBitmap GetDecodedImage() const;
@@ -71,7 +77,7 @@ class NotificationImageLoader
   NotificationImageLoadedCallback callback_;
 
   scoped_ptr<blink::WebURLLoader> url_loader_;
-  int worker_thread_id_;
+  scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner_;
   bool completed_;
 
   std::vector<uint8_t> buffer_;

content/child/notifications/notification_manager.cc

@@ -6,6 +6,7 @@
 
 #include "base/lazy_instance.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/thread_task_runner_handle.h"
 #include "base/threading/thread_local.h"
 #include "content/child/notifications/notification_data_conversions.h"
 #include "content/child/notifications/notification_dispatcher.h"
@@ -212,11 +213,9 @@ scoped_refptr<NotificationImageLoader> NotificationManager::CreateImageLoader(
       new NotificationImageLoader(callback));
 
   main_thread_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&NotificationImageLoader::StartOnMainThread,
-                 pending_notification,
-                 image_url,
-                 CurrentWorkerId()));
+      FROM_HERE, base::Bind(&NotificationImageLoader::StartOnMainThread,
+                            pending_notification, image_url,
+                            base::ThreadTaskRunnerHandle::Get()));
 
   return pending_notification;
 }