Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/page/DOMSelection.cpp

 /*
  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
  * 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 334 matching lines @@
     if (!isValidForPosition(node))
         return;
 
     // FIXME: Eliminate legacy editing positions
     m_frame->selection().setExtent(VisiblePosition(createLegacyEditingPosition(node, offset), DOWNSTREAM));
 }
 
 PassRefPtr<Range> DOMSelection::getRangeAt(int index, ExceptionState& exceptionState)
 {
     if (!m_frame)
-        return 0;
+        return nullptr;
 
     if (index < 0 || index >= rangeCount()) {
         exceptionState.throwDOMException(IndexSizeError, String::number(index) + " is not a valid index.");
-        return 0;
+        return nullptr;
     }
 
     // If you're hitting this, you've added broken multi-range selection support
     ASSERT(rangeCount() == 1);
 
     if (Node* shadowAncestor = selectionShadowAncestor(m_frame)) {
         ASSERT(!shadowAncestor->isShadowRoot());
         ContainerNode* container = shadowAncestor->parentOrShadowHostNode();
         int offset = shadowAncestor->nodeIndex();
         return Range::create(shadowAncestor->document(), container, offset, container, offset);
@@ skipping 160 matching lines @@
 
 bool DOMSelection::isValidForPosition(Node* node) const
 {
     ASSERT(m_frame);
     if (!node)
         return true;
     return node->document() == m_frame->document();
 }
 
 } // namespace WebCore