Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/clipboard/DataTransferItem.cpp

 /*
  * Copyright (C) 2011 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 66 matching lines @@
         return;
     if (!callback || m_item->kind() != DataObjectItem::StringKind)
         return;
 
     StringCallback::scheduleCallback(callback, context, m_item->getAsString());
 }
 
 PassRefPtr<Blob> DataTransferItem::getAsFile() const
 {
     if (!m_clipboard->canReadData())
-        return 0;
+        return nullptr;
 
     return m_item->getAsFile();
 }
 
 DataTransferItem::DataTransferItem(PassRefPtr<Clipboard> clipboard, PassRefPtr<DataObjectItem> item)
     : m_clipboard(clipboard)
     , m_item(item)
 {
     ScriptWrappable::init(this);
 }
 
 
 } // namespace WebCore