Standardize usage of virtual/override/final in mojo/

mojo/services/native_viewport/platform_viewport_headless.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.
 
 #include "base/macros.h"
 #include "mojo/services/native_viewport/platform_viewport.h"
 #include "ui/gfx/rect.h"
 
 namespace mojo {
 
 class PlatformViewportHeadless : public PlatformViewport {
  public:
-  virtual ~PlatformViewportHeadless();
+  ~PlatformViewportHeadless() override;
 
   static scoped_ptr<PlatformViewport> Create(Delegate* delegate);
 
  private:
   explicit PlatformViewportHeadless(Delegate* delegate);
 
   // Overridden from PlatformViewport:
-  virtual void Init(const gfx::Rect& bounds) override;
-  virtual void Show() override;
-  virtual void Hide() override;
-  virtual void Close() override;
-  virtual gfx::Size GetSize() override;
-  virtual void SetBounds(const gfx::Rect& bounds) override;
-  virtual void SetCapture() override;
-  virtual void ReleaseCapture() override;
+  void Init(const gfx::Rect& bounds) override;
+  void Show() override;
+  void Hide() override;
+  void Close() override;
+  gfx::Size GetSize() override;
+  void SetBounds(const gfx::Rect& bounds) override;
+  void SetCapture() override;
+  void ReleaseCapture() override;
 
   Delegate* delegate_;
   gfx::Rect bounds_;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformViewportHeadless);
 };
 
 }  // namespace mojo