IDL: Use Nullable for union type return value

Source/core/html/HTMLOptionsCollection.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 26 matching lines @@
     static PassRefPtrWillBeRawPtr<HTMLOptionsCollection> create(ContainerNode&, CollectionType);
 
     void add(PassRefPtrWillBeRawPtr<HTMLOptionElement>, ExceptionState&);
     void add(PassRefPtrWillBeRawPtr<HTMLOptionElement>, int index, ExceptionState&);
     void remove(int index);
 
     int selectedIndex() const;
     void setSelectedIndex(int);
 
     void setLength(unsigned, ExceptionState&);
-    void namedGetter(const AtomicString& name, bool&, RefPtrWillBeRawPtr<NodeList>&, bool&, RefPtrWillBeRawPtr<Element>&);
+    void namedGetter(const AtomicString& name, RefPtrWillBeRawPtr<NodeList>&, RefPtrWillBeRawPtr<Element>&);
     bool anonymousIndexedSetter(unsigned, PassRefPtrWillBeRawPtr<HTMLOptionElement>, ExceptionState&);
 
 private:
     explicit HTMLOptionsCollection(ContainerNode&);
 
     virtual void supportedPropertyNames(Vector<String>& names) OVERRIDE;
 };
 
 DEFINE_TYPE_CASTS(HTMLOptionsCollection, LiveNodeListBase, collection, collection->type() == SelectOptions, collection.type() == SelectOptions);
 
 } //namespace
 
 #endif