Make IDL Callbacks non-refcounted by default

Source/core/dom/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 46 matching lines @@
     return m_item->kind();
 }
 
 String DataTransferItem::type() const
 {
     if (!m_clipboard->canReadTypes())
         return String();
     return m_item->type();
 }
 
-void DataTransferItem::getAsString(ExecutionContext* context, PassRefPtr<StringCallback> callback) const
+void DataTransferItem::getAsString(ExecutionContext* context, PassOwnPtr<StringCallback> callback) const
 {
     if (!m_clipboard->canReadData())
         return;
 
     m_item->getAsString(callback, context);
 }
 
 PassRefPtr<Blob> DataTransferItem::getAsFile() const
 {
     if (!m_clipboard->canReadData())
         return 0;
 
     return m_item->getAsFile();
 }
 
 DataTransferItem::DataTransferItem(PassRefPtr<Clipboard> clipboard, PassRefPtr<ChromiumDataObjectItem> item)
     : m_clipboard(clipboard)
     , m_item(item)
 {
     ScriptWrappable::init(this);
 }
 
 
 } // namespace WebCore