Add support for [TreatNullAs] extended attribute for reflected attributes

Source/core/html/HTMLFormElement.idl

 /*
  * Copyright (C) 2006, 2010 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 interface HTMLFormElement : HTMLElement {
-    [Reflect=accept_charset] attribute DOMString acceptCharset;
-    [Reflect, URL] attribute DOMString action;
-    [Reflect] attribute DOMString autocomplete;
+    [Reflect=accept_charset, TreatNullAs=NullString] attribute DOMString acceptCharset;
+    [Reflect, TreatNullAs=NullString, URL] attribute DOMString action;
+    [Reflect, TreatNullAs=NullString] attribute DOMString autocomplete;
     [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString enctype;
     [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString encoding;
     [TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString method;
-    [Reflect] attribute DOMString name;
+    [Reflect, TreatNullAs=NullString] attribute DOMString name;
     [Reflect] attribute boolean noValidate;
-    [Reflect] attribute DOMString target;
+    [Reflect, TreatNullAs=NullString] attribute DOMString target;
 
     readonly attribute HTMLCollection elements;
     readonly attribute long length;
     [ImplementedAs=item] getter Node(unsigned long index);
     [ImplementedAs=anonymousNamedGetter, OverrideBuiltins, NotEnumerable] getter (NodeList or Node)(DOMString name);
 
     [ImplementedAs=submitFromJavaScript] void submit();
     [CustomElementCallbacks] void reset();
     boolean checkValidity();
 
     [EnabledAtRuntime=RequestAutocomplete] void requestAutocomplete();
     [EnabledAtRuntime=RequestAutocomplete, NotEnumerable] attribute EventHandler onautocomplete;
     [EnabledAtRuntime=RequestAutocomplete, NotEnumerable] attribute EventHandler onautocompleteerror;
 };