Clean up virtual functions in css/

Source/core/css/CSSCrossfadeValue.h

 /*
  * Copyright (C) 2011 Apple 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 21 matching lines @@
 #include "core/fetch/ImageResourceClient.h"
 #include "core/fetch/ResourcePtr.h"
 #include "platform/graphics/Image.h"
 
 namespace blink {
 
 class ImageResource;
 class CrossfadeSubimageObserverProxy;
 class RenderObject;
 
-class CSSCrossfadeValue : public CSSImageGeneratorValue {
+class CSSCrossfadeValue final : public CSSImageGeneratorValue {
     friend class CrossfadeSubimageObserverProxy;
 public:
     static PassRefPtrWillBeRawPtr<CSSCrossfadeValue> create(PassRefPtrWillBeRawPtr<CSSValue> fromValue, PassRefPtrWillBeRawPtr<CSSValue> toValue)
     {
         return adoptRefWillBeNoop(new CSSCrossfadeValue(fromValue, toValue));
     }
 
     ~CSSCrossfadeValue();
 
     String customCSSText() const;
@@ skipping 24 matching lines @@
         , m_cachedToImage(0)
         , m_crossfadeSubimageObserver(this) { }
 
     class CrossfadeSubimageObserverProxy final : public ImageResourceClient {
     public:
         CrossfadeSubimageObserverProxy(CSSCrossfadeValue* ownerValue)
         : m_ownerValue(ownerValue)
         , m_ready(false) { }
 
         virtual ~CrossfadeSubimageObserverProxy() { }
-        virtual void imageChanged(ImageResource*, const IntRect* = 0) override;
+        virtual void imageChanged(ImageResource*, const IntRect* = nullptr) override;
         void setReady(bool ready) { m_ready = ready; }
     private:
         CSSCrossfadeValue* m_ownerValue;
         bool m_ready;
     };
 
     void crossfadeChanged(const IntRect&);
 
     RefPtrWillBeMember<CSSValue> m_fromValue;
     RefPtrWillBeMember<CSSValue> m_toValue;
     RefPtrWillBeMember<CSSPrimitiveValue> m_percentageValue;
 
     ResourcePtr<ImageResource> m_cachedFromImage;
     ResourcePtr<ImageResource> m_cachedToImage;
 
     RefPtr<Image> m_generatedImage;
 
     CrossfadeSubimageObserverProxy m_crossfadeSubimageObserver;
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSCrossfadeValue, isCrossfadeValue());
 
 } // namespace blink
 
 #endif // CSSCrossfadeValue_h