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

Source/platform/graphics/Canvas2DImageBufferSurface.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 30 matching lines @@
 public:
     Canvas2DImageBufferSurface(const IntSize& size, OpacityMode opacityMode = NonOpaque, int msaaSampleCount = 1)
         : ImageBufferSurface(size, opacityMode)
         , m_layerBridge(Canvas2DLayerBridge::create(size, opacityMode, msaaSampleCount))
     {
         clear();
         if (isValid())
             m_layerBridge->flush();
     }
 
-    virtual ~Canvas2DImageBufferSurface()
+    ~Canvas2DImageBufferSurface() override
     {
         if (m_layerBridge)
             m_layerBridge->beginDestruction();
     }
 
     // ImageBufferSurface implementation
     void finalizeFrame(const FloatRect &dirtyRect) override { m_layerBridge->finalizeFrame(dirtyRect); }
     void willAccessPixels() override { m_layerBridge->willAccessPixels(); }
     SkCanvas* canvas() const override { return m_layerBridge->canvas(); }
     bool isValid() const override { return m_layerBridge && m_layerBridge->checkSurfaceValid(); }
     bool restore() override { return m_layerBridge->restoreSurface(); }
     WebLayer* layer() const override { return m_layerBridge->layer(); }
     bool isAccelerated() const override { return m_layerBridge->isAccelerated(); }
     void setFilterQuality(SkFilterQuality filterQuality) override { m_layerBridge->setFilterQuality(filterQuality); }
     void setIsHidden(bool hidden) override { m_layerBridge->setIsHidden(hidden); }
     void setImageBuffer(ImageBuffer* imageBuffer) override { m_layerBridge->setImageBuffer(imageBuffer); }
     void didDraw(const FloatRect& rect) override { m_layerBridge->didDraw(); }
 
     PassRefPtr<SkImage> newImageSnapshot() const override { return m_layerBridge->newImageSnapshot(); }
 private:
     RefPtr<Canvas2DLayerBridge> m_layerBridge;
 };
 
 } // namespace blink
 
 #endif