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

Source/platform/graphics/StaticBitmapImage.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 StaticBitmapImage_h
 #define StaticBitmapImage_h
 
 #include "platform/graphics/Image.h"
 
 namespace blink {
 
 class PLATFORM_EXPORT StaticBitmapImage : public Image {
 public:
-    virtual ~StaticBitmapImage();
+    ~StaticBitmapImage() override;
 
     bool isImmutableBitmap() override { return true; }
 
     static PassRefPtr<Image> create(PassRefPtr<SkImage>);
     virtual void destroyDecodedData(bool destroyAll) { }
     virtual bool currentFrameKnownToBeOpaque();
     virtual IntSize size() const;
     void draw(SkCanvas*, const SkPaint&, const FloatRect& dstRect, const FloatRect& srcRect, RespectImageOrientationEnum, ImageClampingMode) override;
 
 
     PassRefPtr<SkImage> skImage() override { return m_image; }
 
 protected:
     StaticBitmapImage(PassRefPtr<SkImage>);
 
     RefPtr<SkImage> m_image;
 };
 
 } // namespace blink
 
 #endif