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

ash/system/chromeos/screen_security/screen_share_tray_item.h

 // Copyright 2013 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_SCREEN_SHARE_SCREEN_SHARE_TRAY_ITEM_H_
 #define ASH_SYSTEM_CHROMEOS_SCREEN_SHARE_SCREEN_SHARE_TRAY_ITEM_H_
 
 #include "ash/system/chromeos/screen_security/screen_share_observer.h"
 #include "ash/system/chromeos/screen_security/screen_tray_item.h"
 
 namespace views {
 class View;
 }
 
 namespace ash {
 
 class ASH_EXPORT ScreenShareTrayItem : public ScreenTrayItem,
                                        public ScreenShareObserver {
  public:
   explicit ScreenShareTrayItem(SystemTray* system_tray);
-  virtual ~ScreenShareTrayItem();
+  ~ScreenShareTrayItem() override;
 
  private:
   // Overridden from SystemTrayItem.
-  virtual views::View* CreateTrayView(user::LoginStatus status) override;
-  virtual views::View* CreateDefaultView(user::LoginStatus status) override;
+  views::View* CreateTrayView(user::LoginStatus status) override;
+  views::View* CreateDefaultView(user::LoginStatus status) override;
 
   // Overridden from ScreenTrayItem.
-  virtual void CreateOrUpdateNotification() override;
-  virtual std::string GetNotificationId() override;
+  void CreateOrUpdateNotification() override;
+  std::string GetNotificationId() override;
 
   // Overridden from ScreenShareObserver.
-  virtual void OnScreenShareStart(
-      const base::Closure& stop_callback,
-      const base::string16& helper_name) override;
-  virtual void OnScreenShareStop() override;
+  void OnScreenShareStart(const base::Closure& stop_callback,
+                          const base::string16& helper_name) override;
+  void OnScreenShareStop() override;
 
   base::string16 helper_name_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenShareTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_SCREEN_SHARE_SCREEN_SHARE_TRAY_ITEM_H_