Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/editing/SurroundingText.cpp

 /*
  * Copyright (C) 2012 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 59 matching lines @@
     }
 
     m_positionOffsetInContent = Range::create(*document, backwardsRange->endPosition(), position)->text().length();
     m_contentRange = Range::create(*document, backwardsRange->endPosition(), forwardRange->startPosition());
     ASSERT(m_contentRange);
 }
 
 PassRefPtr<Range> SurroundingText::rangeFromContentOffsets(unsigned startOffsetInContent, unsigned endOffsetInContent)
 {
     if (startOffsetInContent >= endOffsetInContent || endOffsetInContent > content().length())
-        return 0;
+        return nullptr;
 
     CharacterIterator iterator(m_contentRange.get());
 
     ASSERT(!iterator.atEnd());
     iterator.advance(startOffsetInContent);
 
     ASSERT(iterator.range());
     Position start = iterator.range()->startPosition();
 
     ASSERT(!iterator.atEnd());
@@ skipping 12 matching lines @@
         return m_contentRange->text();
     return String();
 }
 
 unsigned SurroundingText::positionOffsetInContent() const
 {
     return m_positionOffsetInContent;
 }
 
 } // namespace WebCore