Revert of Change the update_client task runner behavior to continue on shutdown.

components/update_client/update_client_internal.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 COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_
 
 #include "components/update_client/update_client.h"
 
 #include <queue>
@@ skipping 34 matching lines @@
   void RemoveObserver(Observer* observer) override;
   void Install(const std::string& id,
                const CrxDataCallback& crx_data_callback,
                const CompletionCallback& completion_callback) override;
   void Update(const std::vector<std::string>& ids,
               const CrxDataCallback& crx_data_callback,
               const CompletionCallback& completion_callback) override;
   bool GetCrxUpdateState(const std::string& id,
                          CrxUpdateItem* update_item) const override;
   bool IsUpdating(const std::string& id) const override;
-  void Stop() override;
 
  private:
   ~UpdateClientImpl() override;
 
   void RunTask(scoped_ptr<Task> task);
   void OnTaskComplete(const CompletionCallback& completion_callback,
                       Task* task,
                       int error);
 
   void NotifyObservers(Observer::Events event, const std::string& id);
 
   base::ThreadChecker thread_checker_;
 
-  // True is Stop method has been called.
-  bool is_stopped_;
-
   scoped_refptr<Configurator> config_;
 
   // Contains the tasks that are pending. In the current implementation,
   // only update tasks (background tasks) are queued up. These tasks are
-  // pending while they are in this queue. They have not been picked up yet
-  // by the update engine.
+  // pending while they are in this queue. They are not being handled for
+  // the moment.
   std::queue<Task*> task_queue_;
 
   // Contains all tasks in progress. These are the tasks that the update engine
   // is executing at one moment. Install tasks are run concurrently, update
   // tasks are always serialized, and update tasks are queued up if install
   // tasks are running. In addition, concurrent install tasks for the same id
   // are not allowed.
   std::set<Task*> tasks_;
 
   // TODO(sorin): try to make the ping manager an observer of the service.
   scoped_ptr<PingManager> ping_manager_;
   scoped_ptr<UpdateEngine> update_engine_;
 
   base::ObserverList<Observer> observer_list_;
 
+  // Used to post responses back to the main thread.
+  scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
+
+  // Used to execute blocking tasks.
+  scoped_refptr<base::SequencedTaskRunner> blocking_task_runner_;
+
   DISALLOW_COPY_AND_ASSIGN(UpdateClientImpl);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_