Standardize usage of virtual/override/final specifiers.

ash/system/tray/tray_empty.cc

 // Copyright (c) 2012 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.
 
 #include "ash/system/tray/tray_empty.h"
 
 #include "ui/views/layout/box_layout.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
 #include "ui/views/view.h"
 
 namespace {
 
 class EmptyBackground : public views::Background {
  public:
   EmptyBackground() {}
-  virtual ~EmptyBackground() {}
+  ~EmptyBackground() override {}
 
  private:
-  virtual void Paint(gfx::Canvas* canvas, views::View* view) const override {
-  }
+  void Paint(gfx::Canvas* canvas, views::View* view) const override {}
 
   DISALLOW_COPY_AND_ASSIGN(EmptyBackground);
 };
 
 }
 
 namespace ash {
 
 TrayEmpty::TrayEmpty(SystemTray* system_tray)
     : SystemTrayItem(system_tray) {
@@ skipping 25 matching lines @@
 
 void TrayEmpty::DestroyTrayView() {}
 
 void TrayEmpty::DestroyDefaultView() {}
 
 void TrayEmpty::DestroyDetailedView() {}
 
 void TrayEmpty::UpdateAfterLoginStatusChange(user::LoginStatus status) {}
 
 }  // namespace ash