Adds a SHUTDOWN_TASK_QUEUE and a PreShutdown api to the scheduler.

components/html_viewer/web_scheduler_impl.cc

 // 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.
 
 // An implementation of WebThread in terms of base::MessageLoop and
 // base::Thread
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/tracked_objects.h"
@@ skipping 28 matching lines @@
                                               base::Passed(&scoped_task)));
 }
 
 void WebSchedulerImpl::postTimerTask(
     const blink::WebTraceLocation& web_location,
     blink::WebThread::Task* task,
     long long delayMs) {
   scoped_ptr<blink::WebThread::Task> scoped_task(task);
   tracked_objects::Location location(web_location.functionName(),
                                      web_location.fileName(), -1, nullptr);
-  task_runner_->PostDelayedTask(
+  task_runner_->PostNonNestableDelayedTask(
       location,
       base::Bind(&WebSchedulerImpl::RunTask, base::Passed(&scoped_task)),
       base::TimeDelta::FromMilliseconds(delayMs));
 }
 
+void WebSchedulerImpl::postShutdownTask(
+    const blink::WebTraceLocation& web_location,
+    blink::WebThread::Task* task,
+    long long delayMs) {
+  scoped_ptr<blink::WebThread::Task> scoped_task(task);
+  tracked_objects::Location location(web_location.functionName(),
+                                     web_location.fileName(), -1, nullptr);
+  task_runner_->PostNonNestableDelayedTask(
+      location,
+      base::Bind(&WebSchedulerImpl::RunTask, base::Passed(&scoped_task)),
+      base::TimeDelta::FromMilliseconds(delayMs));
+}
+
+void WebSchedulerImpl::preShutdown() {
+  // TODO(alexclarke) Implement pre shutdown for mojo?
+  NOTIMPLEMENTED();
+}
+
 // static
 void WebSchedulerImpl::RunIdleTask(
     scoped_ptr<blink::WebThread::IdleTask> task) {
   // TODO(davemoore) Implement idle scheduling.
   task->run(0);
 }
 
 // static
 void WebSchedulerImpl::RunTask(scoped_ptr<blink::WebThread::Task> task) {
   task->run();
 }
 
 }  // namespace html_viewer