Introduce a SchedulerHelper in content/child/scheduler

content/renderer/scheduler/cancelable_closure_holder.h

-// Copyright 2014 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_CANCELABLE_CLOSURE_HOLDER_H_
-#define CONTENT_RENDERER_SCHEDULER_CANCELABLE_CLOSURE_HOLDER_H_
-
-#include "base/cancelable_callback.h"
-
-namespace content {
-
-// A CancelableClosureHolder is a CancelableCallback which resets its wrapped
-// callback with a cached closure whenever it is canceled.
-class CancelableClosureHolder {
- public:
-  CancelableClosureHolder();
-  ~CancelableClosureHolder();
-
-  // Resets the closure to be wrapped by the cancelable callback.  Cancels any
-  // outstanding callbacks.
-  void Reset(const base::Closure& callback);
-
-  // Cancels any outstanding closures returned by callback().
-  void Cancel();
-
-  // Returns a callback that will be disabled by calling Cancel(). Callback
-  // must have been set using Reset() before calling this function.
-  const base::Closure& callback() const;
-
- private:
-  base::Closure callback_;
-  base::CancelableClosure cancelable_callback_;
-
-  DISALLOW_COPY_AND_ASSIGN(CancelableClosureHolder);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_RENDERER_SCHEDULER_CANCELABLE_CLOSURE_HOLDER_H_