base: Make ElapsedTimer movable

base/timer/elapsed_timer.h

Index: base/timer/elapsed_timer.h
diff --git a/base/timer/elapsed_timer.h b/base/timer/elapsed_timer.h
index 592858a6e50d225967be99d46940467debad8bf6..9dfa12ccfeb36c752cdfaf7a35746b664bf2c000 100644
--- a/base/timer/elapsed_timer.h
+++ b/base/timer/elapsed_timer.h
@@ -15,6 +15,9 @@ namespace base {
 class BASE_EXPORT ElapsedTimer {
  public:
   ElapsedTimer();
+  ElapsedTimer(ElapsedTimer&& other);
+
+  void operator=(ElapsedTimer&& other);
 
   // Returns the time elapsed since object construction.
   TimeDelta Elapsed() const;