Update platform classes to use OVERRIDE / FINAL when needed

Source/platform/image-decoders/png/PNGImageDecoder.h

 /*
  * Copyright (C) 2006 Apple Computer, 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 class PNGImageReader;
 
 // This class decodes the PNG image format.
 class PLATFORM_EXPORT PNGImageDecoder : public ImageDecoder {
     WTF_MAKE_NONCOPYABLE(PNGImageDecoder);
 public:
     PNGImageDecoder(ImageSource::AlphaOption, ImageSource::GammaAndColorProfileOption, size_t maxDecodedBytes);
     virtual ~PNGImageDecoder();
 
     // ImageDecoder
-    virtual String filenameExtension() const { return "png"; }
-    virtual bool isSizeAvailable();
-    virtual ImageFrame* frameBufferAtIndex(size_t);
+    virtual String filenameExtension() const OVERRIDE { return "png"; }
+    virtual bool isSizeAvailable() OVERRIDE;
+    virtual ImageFrame* frameBufferAtIndex(size_t) OVERRIDE;
     // CAUTION: setFailed() deletes |m_reader|.  Be careful to avoid
     // accessing deleted memory, especially when calling this from inside
     // PNGImageReader!
-    virtual bool setFailed();
+    virtual bool setFailed() OVERRIDE;
 
     // Callbacks from libpng
     void headerAvailable();
     void rowAvailable(unsigned char* rowBuffer, unsigned rowIndex, int interlacePass);
     void pngComplete();
 
     bool isComplete() const
     {
         return !m_frameBufferCache.isEmpty() && (m_frameBufferCache.first().status() == ImageFrame::FrameComplete);
     }
 
 private:
     // Decodes the image.  If |onlySize| is true, stops decoding after
     // calculating the image size.  If decoding fails but there is no more
     // data coming, sets the "decode failure" flag.
     void decode(bool onlySize);
 
     OwnPtr<PNGImageReader> m_reader;
     bool m_doNothingOnFailure;
 };
 
 } // namespace WebCore
 
 #endif