Standardize usage of virtual/override/final specifiers.

ash/system/tray/tray_popup_header_button.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_TRAY_TRAY_POPUP_HEADER_BUTTON_H_
 #define ASH_SYSTEM_TRAY_TRAY_POPUP_HEADER_BUTTON_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/views/controls/button/image_button.h"
 
 namespace ash {
 
 // A ToggleImageButton with fixed size, paddings and hover effects. These
 // buttons are used in the header.
 class ASH_EXPORT TrayPopupHeaderButton : public views::ToggleImageButton {
  public:
   static const char kViewClassName[];
 
   TrayPopupHeaderButton(views::ButtonListener* listener,
                         int enabled_resource_id,
                         int disabled_resource_id,
                         int enabled_resource_id_hover,
                         int disabled_resource_id_hover,
                         int accessible_name_id);
-  virtual ~TrayPopupHeaderButton();
+  ~TrayPopupHeaderButton() override;
 
  private:
   // Overridden from views::View:
-  virtual const char* GetClassName() const override;
-  virtual gfx::Size GetPreferredSize() const override;
-  virtual void OnPaintBorder(gfx::Canvas* canvas) override;
+  const char* GetClassName() const override;
+  gfx::Size GetPreferredSize() const override;
+  void OnPaintBorder(gfx::Canvas* canvas) override;
 
   // Overridden from views::CustomButton:
-  virtual void StateChanged() override;
+  void StateChanged() override;
 
   DISALLOW_COPY_AND_ASSIGN(TrayPopupHeaderButton);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_TRAY_POPUP_HEADER_BUTTON_H_