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

ash/system/chromeos/session/last_window_closed_logout_reminder.h

Index: ash/system/chromeos/session/last_window_closed_logout_reminder.h
diff --git a/ash/system/chromeos/session/last_window_closed_logout_reminder.h b/ash/system/chromeos/session/last_window_closed_logout_reminder.h
index 78e85728d238a34d828fea42049c9a8e7ee4a95a..ad1881604d56877562f12e66ed328fc468f00e78 100644
--- a/ash/system/chromeos/session/last_window_closed_logout_reminder.h
+++ b/ash/system/chromeos/session/last_window_closed_logout_reminder.h
@@ -16,9 +16,9 @@ namespace ash {
 class LastWindowClosedLogoutReminder : public LastWindowClosedObserver {
  public:
   LastWindowClosedLogoutReminder();
-  virtual ~LastWindowClosedLogoutReminder();
+  ~LastWindowClosedLogoutReminder() override;
 
-  virtual void OnLastWindowClosed() override;
+  void OnLastWindowClosed() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LastWindowClosedLogoutReminder);