Fix race in base::Timer when SetTaskRunner() is used

base/timer/timer.h

 // Copyright (c) 2012 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.
 
 // OneShotTimer and RepeatingTimer provide a simple timer API.  As the names
 // suggest, OneShotTimer calls you back once after a time delay expires.
 // RepeatingTimer on the other hand calls you back periodically with the
 // prescribed time interval.
 //
 // OneShotTimer and RepeatingTimer both cancel the timer when they go out of
@@ skipping 136 matching lines @@
   bool is_running() const { return is_running_; }
 
  private:
   friend class BaseTimerTaskInternal;
 
   // Allocates a new |scheduled_task_| and posts it on the current sequence with
   // the given |delay|. |scheduled_task_| must be null. |scheduled_run_time_|
   // and |desired_run_time_| are reset to Now() + delay.
   void PostNewScheduledTask(TimeDelta delay);
 
-  // Returns the task runner on which the task should be scheduled. If the
-  // corresponding |task_runner_| field is null, the task runner for the current
-  // sequence is returned.
-  scoped_refptr<SequencedTaskRunner> GetTaskRunner();
-
   // Disable |scheduled_task_| and abandon it so that it no longer refers back
   // to this object.
   void AbandonScheduledTask();
 
   // Called by BaseTimerTaskInternal when the delayed task fires.
   void RunScheduledTask();
 
   // Stop running task (if any) and abandon scheduled task (if any).
   void AbandonAndStop() {
     AbandonScheduledTask();
@@ skipping 136 matching lines @@
 // to link in MSVC. But clang-plugin does not allow inline definitions of
 // virtual methods, so the inline definition lives in the header file here
 // to satisfy both.
 inline void DelayTimer::Reset() {
   Timer::Reset();
 }
 
 }  // namespace base
 
 #endif  // BASE_TIMER_TIMER_H_