Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/wtf/text/AtomicStringCF.cpp

 /*
  * Copyright (C) 2012 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 18 matching lines @@
 #if USE(CF)
 
 #include "wtf/text/CString.h"
 #include <CoreFoundation/CoreFoundation.h>
 
 namespace WTF {
 
 PassRefPtr<StringImpl> AtomicString::add(CFStringRef string)
 {
     if (!string)
-        return 0;
+        return nullptr;
 
     CFIndex length = CFStringGetLength(string);
 
     if (const LChar* ptr = reinterpret_cast<const LChar*>(CFStringGetCStringPtr(string, kCFStringEncodingISOLatin1)))
         return add(ptr, length);
 
     if (const UniChar* ptr = CFStringGetCharactersPtr(string))
         return add(reinterpret_cast<const UChar*>(ptr), length);
 
     Vector<UniChar, 1024> ucharBuffer(length);
     CFStringGetCharacters(string, CFRangeMake(0, length), ucharBuffer.data());
     return add(reinterpret_cast<const UChar*>(ucharBuffer.data()), length);
 }
 
 } // namespace WTF
 
 #endif // USE(CF)