Replace many [TreatReturnedNullStringAs=Null] with nullable DOMString

Source/core/dom/Attr.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 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,
  * 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 Attr : Node {
 
     // DOM Level 1
 
-    [TreatReturnedNullStringAs=Null] readonly attribute DOMString name;
+    readonly attribute DOMString? name;
 
     [MeasureAs=AttributeSpecified] readonly attribute boolean specified;
 
-    [ImplementedAs=valueForBindings, TreatReturnedNullStringAs=Null, TreatNullAs=NullString, CustomElementCallbacks] attribute DOMString value;
-    [TreatReturnedNullStringAs=Null, TreatNullAs=NullString, DeprecateAs=AttrNodeValue, ImplementedAs=valueForBindings] attribute DOMString nodeValue;
-    [TreatReturnedNullStringAs=Null, TreatNullAs=NullString, DeprecateAs=AttrTextContent, ImplementedAs=valueForBindings] attribute DOMString textContent;
+    [ImplementedAs=valueForBindings, CustomElementCallbacks] attribute DOMString? value;
+    [DeprecateAs=AttrNodeValue, ImplementedAs=valueForBindings] attribute DOMString? nodeValue;
+    [DeprecateAs=AttrTextContent, ImplementedAs=valueForBindings] attribute DOMString? textContent;
 
     // DOM Level 2
 
     [DeprecateAs=AttributeOwnerElement] readonly attribute Element ownerElement;
 
     // DOM 4
 
-    [TreatReturnedNullStringAs=Null] readonly attribute DOMString prefix;
-    [TreatReturnedNullStringAs=Null] readonly attribute DOMString namespaceURI;
-    [TreatReturnedNullStringAs=Null] readonly attribute DOMString localName;
+    readonly attribute DOMString? prefix;
+    readonly attribute DOMString? namespaceURI;
+    readonly attribute DOMString? localName;
 };