Adds a SHUTDOWN_TASK_QUEUE and a PreShutdown api to the scheduler.

components/scheduler/child/task_queue_manager.cc

 // 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.
 
 #include "components/scheduler/child/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 531 matching lines @@
   internal::TaskQueue* queue = Queue(queue_index);
   queue->SetPumpPolicy(pump_policy);
 }
 
 void TaskQueueManager::PumpQueue(size_t queue_index) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::TaskQueue* queue = Queue(queue_index);
   queue->PumpQueue();
 }
 
+void TaskQueueManager::FlushQueue(size_t queue_index) {
+  internal::TaskQueue* queue = Queue(queue_index);
+  queue->WillDeleteTaskQueueManager();
+}
+
 bool TaskQueueManager::UpdateWorkQueues(
     const base::PendingTask* previous_task) {
   // TODO(skyostil): This is not efficient when the number of queues grows very
   // large due to the number of locks taken. Consider optimizing when we get
   // there.
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::LazyNow lazy_now(this);
   bool has_work = false;
   for (auto& queue : queues_) {
     has_work |= queue->UpdateWorkQueue(&lazy_now, previous_task);
@@ skipping 173 matching lines @@
     state->SetInteger("selected_queue", selected_queue);
   return state;
 }
 
 void TaskQueueManager::OnTaskQueueEnabled() {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   MaybePostDoWorkOnMainRunner();
 }
 
 }  // namespace scheduler