Revert of scheduler: Implement task observers

content/renderer/scheduler/webthread_impl_for_scheduler.h

-// Copyright 2015 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 CONTENT_RENDERER_SCHEDULER_WEBTHREAD_IMPL_FOR_SCHEDULER_H_
-#define CONTENT_RENDERER_SCHEDULER_WEBTHREAD_IMPL_FOR_SCHEDULER_H_
-
-#include "content/child/webthread_impl.h"
-
-namespace content {
-
-class RendererScheduler;
-
-class WebThreadImplForScheduler : public WebThreadBase {
- public:
-  CONTENT_EXPORT explicit WebThreadImplForScheduler(
-      RendererScheduler* scheduler);
-  CONTENT_EXPORT virtual ~WebThreadImplForScheduler();
-
-  // blink::WebThread implementation.
-  blink::PlatformThreadId threadId() const override;
-
-  // WebThreadBase implementation.
-  base::SingleThreadTaskRunner* TaskRunner() const override;
-
- private:
-  base::MessageLoop* MessageLoop() const override;
-
-  void AddTaskObserverInternal(
-      base::MessageLoop::TaskObserver* observer) override;
-  void RemoveTaskObserverInternal(
-      base::MessageLoop::TaskObserver* observer) override;
-
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  RendererScheduler* scheduler_;  // Not owned.
-  blink::PlatformThreadId thread_id_;
-};
-
-}  // namespace content
-
-#endif  // CONTENT_RENDERER_SCHEDULER_WEBTHREAD_IMPL_FOR_SCHEDULER_H_