Clean up virtual functions in css/

Source/core/css/CSSBorderImageSliceValue.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 23 matching lines @@
 
 class CSSBorderImageSliceValue : public CSSValue {
 public:
     static PassRefPtrWillBeRawPtr<CSSBorderImageSliceValue> create(PassRefPtrWillBeRawPtr<CSSPrimitiveValue> slices, bool fill)
     {
         return adoptRefWillBeNoop(new CSSBorderImageSliceValue(slices, fill));
     }
 
     String customCSSText() const;
 
-    Quad* slices() { return m_slices ? m_slices->getQuadValue() : 0; }
+    Quad* slices() { return m_slices ? m_slices->getQuadValue() : nullptr; }
 
     bool equals(const CSSBorderImageSliceValue&) const;
 
     void traceAfterDispatch(Visitor*);
 
     // These four values are used to make "cuts" in the border image. They can be numbers
     // or percentages.
     RefPtrWillBeMember<CSSPrimitiveValue> m_slices;
     bool m_fill;
 
 private:
     CSSBorderImageSliceValue(PassRefPtrWillBeRawPtr<CSSPrimitiveValue> slices, bool fill);
 };
 
 DEFINE_CSS_VALUE_TYPE_CASTS(CSSBorderImageSliceValue, isBorderImageSliceValue());
 
 } // namespace blink
 
 #endif // CSSBorderImageSliceValue_h