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

components/update_client/task_update.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_TASK_UPDATE_H_
 #define COMPONENTS_UPDATE_CLIENT_TASK_UPDATE_H_
 
 #include <queue>
 #include <string>
 #include <vector>
@@ skipping 22 matching lines @@
   //    this task when the task is done.
   TaskUpdate(UpdateEngine* update_engine,
              bool is_foreground,
              const std::vector<std::string>& ids,
              const UpdateClient::CrxDataCallback& crx_data_callback,
              const Callback& callback);
   ~TaskUpdate() override;
 
   void Run() override;
 
-  void Cancel() override;
-
   std::vector<std::string> GetIds() const override;
 
  private:
-  // Called when the task has completed either because the task has run or
-  // it has been canceled.
-  void TaskComplete(int error);
+  // Called when the Run function associated with this task has completed.
+  void RunComplete(int error);
 
   base::ThreadChecker thread_checker_;
 
   UpdateEngine* update_engine_;  // Not owned by this class.
 
   const bool is_foreground_;
   const std::vector<std::string> ids_;
   const UpdateClient::CrxDataCallback crx_data_callback_;
   const Callback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskUpdate);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_TASK_UPDATE_H_