Make SyncTaskManager's regular Task cancellable (like SyncTask)

chrome/browser/sync_file_system/sync_task_manager.h

 // Copyright 2013 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 CHROME_BROWSER_SYNC_FILE_SYSTEM_SYNC_TASK_MANAGER_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_SYNC_TASK_MANAGER_H_
 
 #include <deque>
 
 #include "base/callback.h"
@@ skipping 30 matching lines @@
   };
 
   explicit SyncTaskManager(base::WeakPtr<Client> client);
   virtual ~SyncTaskManager();
 
   // This needs to be called to start task scheduling.
   // If |status| is not SYNC_STATUS_OK calling this may change the
   // service status. This should not be called more than once.
   void Initialize(SyncStatusCode status);
 
-  // Note that the argument of |task|'s parameter owns |callback|.
-  // The reference from |callback| to |task| causes circular dependency.
   void ScheduleTask(const Task& task,
                     const SyncStatusCallback& callback);
   void ScheduleSyncTask(scoped_ptr<SyncTask> task,
                         const SyncStatusCallback& callback);
 
   // Runs the posted task only when we're idle.
   void ScheduleTaskIfIdle(const Task& task);
   void ScheduleSyncTaskIfIdle(scoped_ptr<SyncTask> task);
 
   void NotifyTaskDone(scoped_ptr<TaskToken> token,
-                      const SyncStatusCallback& callback,
                       SyncStatusCode status);
 
  private:
   // This should be called when an async task needs to get a task token.
   scoped_ptr<TaskToken> GetToken(const tracked_objects::Location& from_here);
 
   // Creates a completion callback that calls NotifyTaskDone.
   // It is ok to give null |callback|.
   SyncStatusCallback CreateCompletionCallback(
       scoped_ptr<TaskToken> token,
       const SyncStatusCallback& callback);
 
   base::WeakPtr<Client> client_;
 
   SyncStatusCode last_operation_status_;
   scoped_ptr<SyncTask> running_task_;
   std::deque<base::Closure> pending_tasks_;
+  SyncStatusCallback current_callback_;
+
 
   // Absence of |token_| implies a task is running. Incoming tasks should
   // wait for the task to finish in |pending_tasks_| if |token_| is null.
   // Each task must take TaskToken instance from |token_| and must hold it
   // until it finished. And the task must return the instance through
   // NotifyTaskDone when the task finished.
   scoped_ptr<TaskToken> token_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncTaskManager);
 };
 
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_SYNC_TASK_MANAGER_H_