Clean up virtual functions in css/

Source/core/css/CSSFontFaceSource.h

 /*
  * Copyright (C) 2007, 2008, 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 27 matching lines @@
 
 class CSSFontFaceSource : public NoBaseWillBeGarbageCollectedFinalized<CSSFontFaceSource> {
 public:
     virtual ~CSSFontFaceSource();
 
     virtual bool isLocal() const { return false; }
     virtual bool isLoading() const { return false; }
     virtual bool isLoaded() const { return true; }
     virtual bool isValid() const { return true; }
 
-    virtual FontResource* resource() { return 0; }
+    virtual FontResource* resource() { return nullptr; }
     void setFontFace(CSSFontFace* face) { m_face = face; }
 
     PassRefPtr<SimpleFontData> getFontData(const FontDescription&);
 
     virtual bool isLocalFontAvailable(const FontDescription&) { return false; }
     virtual void beginLoadIfNeeded() { }
 
     // For UMA reporting
     virtual bool hadBlankText() { return false; }
 
     virtual void trace(Visitor*);
 
 protected:
     CSSFontFaceSource();
     virtual PassRefPtr<SimpleFontData> createFontData(const FontDescription&) = 0;
 
     typedef HashMap<unsigned, RefPtr<SimpleFontData> > FontDataTable; // The hash key is composed of size synthetic styles.
 
     RawPtrWillBeMember<CSSFontFace> m_face; // Our owning font face.
     FontDataTable m_fontDataTable;
 };
 
 }
 
 #endif