scheduler: Implement task observers

content/child/webthread_impl.h

Index: content/child/webthread_impl.h
diff --git a/content/child/webthread_impl.h b/content/child/webthread_impl.h
index ba2888f9bc70b007789d3f8ce022234ec45c3f33..576e6a4a1065217b0a3b675d5e6295c846ffbe21 100644
--- a/content/child/webthread_impl.h
+++ b/content/child/webthread_impl.h
@@ -29,11 +29,18 @@ class CONTENT_EXPORT WebThreadBase : public blink::WebThread {
   virtual blink::PlatformThreadId threadId() const = 0;
 
  protected:
+  class TaskObserverAdapter;
+
   WebThreadBase();
 
- private:
-  class TaskObserverAdapter;
+  virtual void AddTaskObserverInternal(
+      base::MessageLoop::TaskObserver* observer);
+  virtual void RemoveTaskObserverInternal(
+      base::MessageLoop::TaskObserver* observer);
+
+  static void RunWebThreadTask(scoped_ptr<blink::WebThread::Task> task);
 
+ private:
   typedef std::map<TaskObserver*, TaskObserverAdapter*> TaskObserverMap;
   TaskObserverMap task_observer_map_;
 };