Fix virtual/override/final usage in Source/platform/.

Source/platform/graphics/UnacceleratedImageBufferSurface.h

 /*
  * Copyright (c) 2013, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 24 matching lines @@
 #include "wtf/RefPtr.h"
 
 class SkSurface;
 
 namespace blink {
 
 class PLATFORM_EXPORT UnacceleratedImageBufferSurface : public ImageBufferSurface {
     WTF_MAKE_NONCOPYABLE(UnacceleratedImageBufferSurface); WTF_MAKE_FAST_ALLOCATED(UnacceleratedImageBufferSurface);
 public:
     UnacceleratedImageBufferSurface(const IntSize&, OpacityMode = NonOpaque);
-    virtual ~UnacceleratedImageBufferSurface();
+    ~UnacceleratedImageBufferSurface() override;
 
-    virtual SkCanvas* canvas() const override;
-    virtual bool isValid() const override;
+    SkCanvas* canvas() const override;
+    bool isValid() const override;
 
-    virtual PassRefPtr<SkImage> newImageSnapshot() const override;
+    PassRefPtr<SkImage> newImageSnapshot() const override;
 private:
     RefPtr<SkSurface> m_surface;
 };
 
 } // namespace blink
 
 #endif