Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/frame/PageConsole.h

 /*
  * Copyright (C) 2013 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
@@ skipping 32 matching lines @@
 // console messages and routes them up through the
 // FrameHost to the ChromeClient and Inspector.
 // It's meant as an abstraction around ChromeClient calls
 // and the way that Blink core/ can add messages to the console.
 
 class PageConsole FINAL {
 public:
     static PassOwnPtr<PageConsole> create(FrameHost& host) { return adoptPtr(new PageConsole(host)); }
 
     void addMessage(MessageSource, MessageLevel, const String& message);
-    void addMessage(MessageSource, MessageLevel, const String& message, const String& sourceURL, unsigned lineNumber, unsigned columnNumber = 0, PassRefPtr<ScriptCallStack> = 0, ScriptState* = 0, unsigned long requestIdentifier = 0);
+    void addMessage(MessageSource, MessageLevel, const String& message, const String& sourceURL, unsigned lineNumber, unsigned columnNumber = 0, PassRefPtr<ScriptCallStack> = nullptr, ScriptState* = 0, unsigned long requestIdentifier = 0);
     void addMessage(MessageSource, MessageLevel, const String& message, PassRefPtr<ScriptCallStack>);
     static String formatStackTraceString(const String& originalMessage, PassRefPtr<ScriptCallStack>);
 
     static void mute();
     static void unmute();
 
 private:
     explicit PageConsole(FrameHost&);
 
     FrameHost& m_frameHost;
 };
 
 } // namespace WebCore
 
 #endif // PageConsole_h