Standardize usage of virtual/override/final in mojo/

mojo/cc/direct_output_surface.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 MOJO_CC_DIRECT_OUTPUT_SURFACE_H_
 #define MOJO_CC_DIRECT_OUTPUT_SURFACE_H_
 
 #include "cc/output/output_surface.h"
 
 namespace mojo {
 
 // An OutputSurface implementation that directly draws and
 // swaps to an actual GL surface.
 class DirectOutputSurface : public cc::OutputSurface {
  public:
   explicit DirectOutputSurface(
       const scoped_refptr<cc::ContextProvider>& context_provider);
-  virtual ~DirectOutputSurface() override;
+  ~DirectOutputSurface() override;
 
   // cc::OutputSurface implementation
-  virtual void SwapBuffers(cc::CompositorFrame* frame) override;
+  void SwapBuffers(cc::CompositorFrame* frame) override;
 
 private:
   base::WeakPtrFactory<DirectOutputSurface> weak_ptr_factory_;
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_CC_DIRECT_OUTPUT_SURFACE_H_