Adds a SHUTDOWN_TASK_QUEUE and a PreShutdown api to the scheduler.

components/scheduler/child/web_scheduler_impl.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_BASE_WEB_SCHEDULER_IMPL_H_
 #define CONTENT_CHILD_SCHEDULER_BASE_WEB_SCHEDULER_IMPL_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "components/scheduler/scheduler_export.h"
 #include "third_party/WebKit/public/platform/WebScheduler.h"
 #include "third_party/WebKit/public/platform/WebThread.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace scheduler {
 
 class ChildScheduler;
 class SingleThreadIdleTaskRunner;
 
 class SCHEDULER_EXPORT WebSchedulerImpl : public blink::WebScheduler {
  public:
   WebSchedulerImpl(
       ChildScheduler* child_scheduler,
       scoped_refptr<SingleThreadIdleTaskRunner> idle_task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> loading_task_runner,
-      scoped_refptr<base::SingleThreadTaskRunner> timer_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> timer_task_runner,
+      scoped_refptr<base::SingleThreadTaskRunner> shutdown_task_runner);
   ~WebSchedulerImpl() override;
 
   // blink::WebScheduler implementation:
   virtual bool shouldYieldForHighPriorityWork();
   virtual bool canExceedIdleDeadlineIfRequired();
+  virtual void preShutdown();
   virtual void postIdleTask(const blink::WebTraceLocation& location,
                             blink::WebThread::IdleTask* task);
   virtual void postNonNestableIdleTask(const blink::WebTraceLocation& location,
                                        blink::WebThread::IdleTask* task);
   virtual void postIdleTaskAfterWakeup(const blink::WebTraceLocation& location,
                                        blink::WebThread::IdleTask* task);
   virtual void postLoadingTask(const blink::WebTraceLocation& location,
                                blink::WebThread::Task* task);
   virtual void postTimerTask(const blink::WebTraceLocation& location,
                              blink::WebThread::Task* task,
                              long long delayMs);
+  virtual void postShutdownTask(const blink::WebTraceLocation& location,
+                                blink::WebThread::Task* task,
+                                long long delayMs);
 
  private:
   static void runIdleTask(scoped_ptr<blink::WebThread::IdleTask> task,
                           base::TimeTicks deadline);
   static void runTask(scoped_ptr<blink::WebThread::Task> task);
 
   ChildScheduler* child_scheduler_;  // NOT OWNED
   scoped_refptr<SingleThreadIdleTaskRunner> idle_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> loading_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> timer_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> shutdown_task_runner_;
 };
 
 }  // namespace scheduler
 
 #endif  // CONTENT_CHILD_SCHEDULER_BASE_WEB_SCHEDULER_IMPL_H_