Update {virtual,override,final} to follow C++11 style in ui.

ui/chromeos/user_activity_power_manager_notifier.h

Index: ui/chromeos/user_activity_power_manager_notifier.h
diff --git a/ui/chromeos/user_activity_power_manager_notifier.h b/ui/chromeos/user_activity_power_manager_notifier.h
index 0d3e4e223fe4da0c79cbad0661e26e834efd2d7a..1f7babd283b57d3795c7411784063d0b2f08ab66 100644
--- a/ui/chromeos/user_activity_power_manager_notifier.h
+++ b/ui/chromeos/user_activity_power_manager_notifier.h
@@ -20,10 +20,10 @@ class UI_CHROMEOS_EXPORT UserActivityPowerManagerNotifier
     : public UserActivityObserver {
  public:
   explicit UserActivityPowerManagerNotifier(UserActivityDetector* detector);
-  virtual ~UserActivityPowerManagerNotifier();
+  ~UserActivityPowerManagerNotifier() override;
 
   // UserActivityObserver implementation.
-  virtual void OnUserActivity(const Event* event) override;
+  void OnUserActivity(const Event* event) override;
 
  private:
   UserActivityDetector* detector_;  // not owned