Adds a SHUTDOWN_TASK_QUEUE and a PreShutdown api to the scheduler.

components/scheduler/child/task_queue_manager.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_TASK_QUEUE_MANAGER_H_
 #define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
 
 #include "base/atomic_sequence_num.h"
 #include "base/debug/task_annotator.h"
 #include "base/macros.h"
@@ skipping 109 matching lines @@
   // manager executes its tasks on.
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
   void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
 
   void SetTimeSourceForTesting(scoped_ptr<TimeSource> time_source);
 
   // Returns a bitmap where a bit is set iff a task on the corresponding queue
   // was run since the last call to GetAndClearTaskWasRunOnQueueBitmap.
   uint64 GetAndClearTaskWasRunOnQueueBitmap();
 
+  void FlushQueue(size_t queue_index);
+
  private:
   // TaskQueueSelector::Observer implementation:
   void OnTaskQueueEnabled() override;
 
   friend class internal::LazyNow;
   friend class internal::TaskQueue;
 
   class DeletionSentinel : public base::RefCounted<DeletionSentinel> {
    private:
     friend class base::RefCounted<DeletionSentinel>;
@@ skipping 76 matching lines @@
 
   scoped_refptr<DeletionSentinel> deletion_sentinel_;
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace scheduler
 
 #endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_