Implement ParentNode IDL interface

Source/core/html/HTMLElement.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
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              [TreatNullAs=NullString, SetterRaisesException] attribute DOMString outerText;
 
     [RaisesException] Element insertAdjacentElement([Default=Undefined] optional DOMString where,
                                   [Default=Undefined] optional Element element);
     [DeliverCustomElementCallbacks, RaisesException] void insertAdjacentHTML([Default=Undefined] optional DOMString where,
                             [Default=Undefined] optional DOMString html);
     [RaisesException] void insertAdjacentText([Default=Undefined] optional DOMString where,
                             [Default=Undefined] optional DOMString text);
 
     [EnabledAtRuntime=imeAPI] InputMethodContext getInputContext();
-    readonly attribute HTMLCollection children;
 
              [TreatNullAs=NullString, SetterRaisesException] attribute DOMString contentEditable;
     readonly attribute boolean isContentEditable;
 
              attribute boolean spellcheck;
 
     void click();
 };