Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/editing/TypingCommand.cpp

 /*
  * Copyright (C) 2005, 2006, 2007, 2008 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 215 matching lines @@
 
     TypingCommand::create(document, InsertParagraphSeparator, "", options)->apply();
 }
 
 PassRefPtr<TypingCommand> TypingCommand::lastTypingCommandIfStillOpenForTyping(Frame* frame)
 {
     ASSERT(frame);
 
     RefPtr<CompositeEditCommand> lastEditCommand = frame->editor().lastEditCommand();
     if (!lastEditCommand || !lastEditCommand->isTypingCommand() || !static_cast<TypingCommand*>(lastEditCommand.get())->isOpenForMoreTyping())
-        return 0;
+        return nullptr;
 
     return static_cast<TypingCommand*>(lastEditCommand.get());
 }
 
 void TypingCommand::closeTyping(Frame* frame)
 {
     if (RefPtr<TypingCommand> lastTypingCommand = lastTypingCommandIfStillOpenForTyping(frame))
         lastTypingCommand->closeTyping();
 }
 
@@ skipping 371 matching lines @@
     ASSERT_NOT_REACHED();
     m_preservesTypingStyle = false;
 }
 
 bool TypingCommand::isTypingCommand() const
 {
     return true;
 }
 
 } // namespace WebCore