base: Make ElapsedTimer movable

base/timer/elapsed_timer.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 BASE_TIMER_ELAPSED_TIMER_H_
 #define BASE_TIMER_ELAPSED_TIMER_H_
 
 #include "base/base_export.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 
 namespace base {
 
 // A simple wrapper around TimeTicks::Now().
 class BASE_EXPORT ElapsedTimer {
  public:
   ElapsedTimer();
+  ElapsedTimer(ElapsedTimer&& other);
+
+  void operator=(ElapsedTimer&& other);
 
   // Returns the time elapsed since object construction.
   TimeDelta Elapsed() const;
 
  private:
   TimeTicks begin_;
 
   DISALLOW_COPY_AND_ASSIGN(ElapsedTimer);
 };
 
 }  // namespace base
 
 #endif  // BASE_TIMER_ELAPSED_TIMER_H_