Use union types for HTMLSelectElement.add()'s arguments

Source/core/html/HTMLOptionsCollection.idl

 /*
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2013, 2014 Samsung Electronics. 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 13 matching lines @@
     SetWrapperReferenceFrom=ownerNode,
 ] interface HTMLOptionsCollection : HTMLCollection {
     attribute long selectedIndex;
     [Custom=Setter, RaisesException=Setter] attribute unsigned long length;
     [ImplementedAs=item] getter Node (unsigned long index);
     [RaisesException, TypeChecking=Interface] setter HTMLOptionElement (unsigned long index, HTMLOptionElement? value);
 
     // FIXME: The spec and firefox return an Element (the first matching Element).
     [ImplementedAs=namedGetter] getter (NodeList or Element)? namedItem(DOMString name);
 
-    [Custom, RaisesException] void add([Default=Undefined] optional HTMLOptionElement option, optional unsigned long index);
+    [RaisesException, TypeChecking=Interface] void add((HTMLOptionElement or HTMLOptGroupElement) element,
+                                                       optional (HTMLElement or long)? before = null);
     void remove(unsigned long index);
 };