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

ash/system/chromeos/session/tray_session_length_limit.h

 // Copyright 2014 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.
 
 #ifndef ASH_SYSTEM_CHROMEOS_SESSION_SESSION_LENGTH_LIMIT_H_
 #define ASH_SYSTEM_CHROMEOS_SESSION_SESSION_LENGTH_LIMIT_H_
 
 #include "ash/system/chromeos/session/session_length_limit_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/basictypes.h"
@@ skipping 14 matching lines @@
 class ASH_EXPORT TraySessionLengthLimit : public SystemTrayItem,
                                           public SessionLengthLimitObserver {
 public:
   enum LimitState {
     LIMIT_NONE,
     LIMIT_SET,
     LIMIT_EXPIRING_SOON
   };
 
   explicit TraySessionLengthLimit(SystemTray* system_tray);
-  virtual ~TraySessionLengthLimit();
+  ~TraySessionLengthLimit() override;
 
   // SystemTrayItem:
-  virtual views::View* CreateDefaultView(user::LoginStatus status) override;
-  virtual void DestroyDefaultView() override;
+  views::View* CreateDefaultView(user::LoginStatus status) override;
+  void DestroyDefaultView() override;
 
   // SessionLengthLimitObserver:
-  virtual void OnSessionStartTimeChanged() override;
-  virtual void OnSessionLengthLimitChanged() override;
+  void OnSessionStartTimeChanged() override;
+  void OnSessionLengthLimitChanged() override;
 
  private:
   friend class test::TraySessionLengthLimitTest;
 
   static const char kNotificationId[];
 
   // Update state, notification and tray bubble view.  Called by the
   // RepeatingTimer in regular intervals and also by OnSession*Changed().
   void Update();
 
@@ skipping 16 matching lines @@
 
   LabelTrayView* tray_bubble_view_;
   scoped_ptr<base::RepeatingTimer<TraySessionLengthLimit> > timer_;
 
   DISALLOW_COPY_AND_ASSIGN(TraySessionLengthLimit);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_SESSION_SESSION_LENGTH_LIMIT_H_