Change base::TickClock to a ref counted class.

ash/system/chromeos/session/logout_confirmation_controller.h

Index: ash/system/chromeos/session/logout_confirmation_controller.h
diff --git a/ash/system/chromeos/session/logout_confirmation_controller.h b/ash/system/chromeos/session/logout_confirmation_controller.h
index e24406933d09ab0626e2860ba3694ac268bd3e5a..84e973cf2eb21d36e2368c8b3f06b5b71fb393ed 100644
--- a/ash/system/chromeos/session/logout_confirmation_controller.h
+++ b/ash/system/chromeos/session/logout_confirmation_controller.h
@@ -40,7 +40,7 @@ class ASH_EXPORT LogoutConfirmationController : public ShellObserver {
   // the current dialog's |logout_time_|.
   void ConfirmLogout(base::TimeTicks logout_time);
 
-  void SetClockForTesting(scoped_ptr<base::TickClock> clock);
+  void SetClockForTesting(const scoped_refptr<base::TickClock>& clock);
 
   // ShellObserver:
   virtual void OnLockStateChanged(bool locked) override;
@@ -54,7 +54,7 @@ class ASH_EXPORT LogoutConfirmationController : public ShellObserver {
   LogoutConfirmationDialog* dialog_for_testing() const { return dialog_; }
 
  private:
-  scoped_ptr<base::TickClock> clock_;
+  scoped_refptr<base::TickClock> clock_;
   base::Closure logout_closure_;
 
   base::TimeTicks logout_time_;