base: Make ElapsedTimer movable

base/timer/elapsed_timer.cc

 // 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.
 
 #include "base/timer/elapsed_timer.h"
 
 namespace base {
 
 ElapsedTimer::ElapsedTimer() {
   begin_ = TimeTicks::Now();
 }
 
+ElapsedTimer::ElapsedTimer(ElapsedTimer&& other) {
+  begin_ = other.begin_;
+}
+
+void ElapsedTimer::operator=(ElapsedTimer&& other) {
+  begin_ = other.begin_;
+}
+
 TimeDelta ElapsedTimer::Elapsed() const {
   return TimeTicks::Now() - begin_;
 }
 
 }  // namespace base