Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/editing/IndentOutdentCommand.cpp

 /*
  * Copyright (C) 2006, 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 220 matching lines @@
 {
     if (m_typeOfAction == Indent)
         ApplyBlockElementCommand::formatSelection(startOfSelection, endOfSelection);
     else
         outdentRegion(startOfSelection, endOfSelection);
 }
 
 void IndentOutdentCommand::formatRange(const Position& start, const Position& end, const Position&, RefPtr<Element>& blockquoteForNextIndent)
 {
     if (tryIndentingAsListItem(start, end))
-        blockquoteForNextIndent = 0;
+        blockquoteForNextIndent = nullptr;
     else
         indentIntoBlockquote(start, end, blockquoteForNextIndent);
 }
 
 }