Move blink scheduler implementation into a component

content/child/scheduler/child_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_CHILD_SCHEDULER_CHILD_SCHEDULER_H_
-#define CONTENT_CHILD_SCHEDULER_CHILD_SCHEDULER_H_
-
-#include "base/message_loop/message_loop.h"
-#include "content/child/scheduler/single_thread_idle_task_runner.h"
-#include "content/common/content_export.h"
-
-namespace base {
-class MessageLoop;
-}
-
-namespace content {
-
-class CONTENT_EXPORT ChildScheduler {
- public:
-  virtual ~ChildScheduler() { }
-
-  // Returns the default task runner.
-  virtual scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() = 0;
-
-  // Returns the idle task runner. Tasks posted to this runner may be reordered
-  // relative to other task types and may be starved for an arbitrarily long
-  // time if no idle time is available.
-  virtual scoped_refptr<SingleThreadIdleTaskRunner> IdleTaskRunner() = 0;
-
-  // Returns true if there is high priority work pending on the main thread
-  // and the caller should yield to let the scheduler service that work. Note
-  // that this is a stricter condition than |IsHighPriorityWorkAnticipated|,
-  // restricted to the case where real work is pending.
-  // Must be called from the thread this scheduler was created on.
-  virtual bool ShouldYieldForHighPriorityWork() = 0;
-
-  // Returns true if a currently running idle task could exceed its deadline
-  // without impacting user experience too much. This should only be used if
-  // there is a task which cannot be pre-empted and is likely to take longer
-  // than the largest expected idle task deadline. It should NOT be polled to
-  // check whether more work can be performed on the current idle task after
-  // its deadline has expired - post a new idle task for the continuation of the
-  // work in this case.
-  // Must be called from the thread this scheduler was created on.
-  virtual bool CanExceedIdleDeadlineIfRequired() const = 0;
-
-  // Adds or removes a task observer from the scheduler. The observer will be
-  // notified before and after every executed task. These functions can only be
-  // called on the thread this scheduler was created on.
-  virtual void AddTaskObserver(
-      base::MessageLoop::TaskObserver* task_observer) = 0;
-  virtual void RemoveTaskObserver(
-      base::MessageLoop::TaskObserver* task_observer) = 0;
-
-  // Shuts down the scheduler by dropping any remaining pending work in the work
-  // queues. After this call any work posted to the task runners will be
-  // silently dropped.
-  virtual void Shutdown() = 0;
-
- protected:
-  ChildScheduler() { }
-  DISALLOW_COPY_AND_ASSIGN(ChildScheduler);
-};
-
-}  // namespace content
-
-#endif  // CONTENT_CHILD_SCHEDULER_CHILD_SCHEDULER_H_