Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/editing/PlainTextRange.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov.
  *
  * 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 129 matching lines @@
                 else
                     resultRange->setEnd(textRunRange->endContainer(), textRunRange->endOffset(), IGNORE_EXCEPTION);
             }
             docTextPosition += len;
             break;
         }
         docTextPosition += len;
     }
 
     if (!startRangeFound)
-        return 0;
+        return nullptr;
 
     if (length() && end() > docTextPosition) { // end() is out of bounds
         resultRange->setEnd(textRunRange->endContainer(), textRunRange->endOffset(), IGNORE_EXCEPTION);
     }
 
     return resultRange.release();
 }
 
 PlainTextRange PlainTextRange::create(const Node& scope, const Range& range)
 {
@@ skipping 15 matching lines @@
     size_t start = TextIterator::rangeLength(testRange.get());
 
     testRange->setEnd(range.endContainer(), range.endOffset(), IGNORE_EXCEPTION);
     ASSERT(testRange->startContainer() == &scope);
     size_t end = TextIterator::rangeLength(testRange.get());
 
     return PlainTextRange(start, end);
 }
 
 }