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

components/update_client/update_client_internal.h

Index: components/update_client/update_client_internal.h
diff --git a/components/update_client/update_client_internal.h b/components/update_client/update_client_internal.h
index 0dc98be13b4a736b326d004cf39c3481345f71b8..6a5bf39b7cc0053a97c983900323aecdee98a93b 100644
--- a/components/update_client/update_client_internal.h
+++ b/components/update_client/update_client_internal.h
@@ -52,6 +52,7 @@
   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;
@@ -65,12 +66,15 @@
 
   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 are not being handled for
-  // the moment.
+  // pending while they are in this queue. They have not been picked up yet
+  // by the update engine.
   std::queue<Task*> task_queue_;
 
   // Contains all tasks in progress. These are the tasks that the update engine
@@ -86,12 +90,6 @@
 
   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);
 };