Make Attr.localName/name and Element.localName/tagName not nullable

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.
  */
 
 // https://dom.spec.whatwg.org/#interface-attr
 
 // FIXME: Attr should not inherit from Node. crbug.com/305105
 interface Attr : Node {
     readonly attribute DOMString? namespaceURI;
     readonly attribute DOMString? prefix;
-    // FIXME: localName/name/value/nodeValue/textContent should not be nullable.
-    readonly attribute DOMString? localName;
-    readonly attribute DOMString? name;
+    readonly attribute DOMString localName;
+    readonly attribute DOMString name;
+    // FIXME: value/nodeValue/textContent should not be nullable.
     [ImplementedAs=valueForBindings, CustomElementCallbacks] attribute DOMString? value;
     [ImplementedAs=valueForBindings, MeasureAs=AttrNodeValue] attribute DOMString? nodeValue; // legacy alias of .value
     [ImplementedAs=valueForBindings, MeasureAs=AttrTextContent] attribute DOMString? textContent; // legacy alias of .value
 
     [MeasureAs=AttributeOwnerElement] readonly attribute Element? ownerElement;
 
     [MeasureAs=AttributeSpecified] readonly attribute boolean specified; // useless; always returns true
 
     // FIXME: Attr should not have any child nodes. crbug.com/305105
     [DeprecateAs=AttrChildAccess] readonly attribute NodeList childNodes;
     [DeprecateAs=AttrChildAccess] readonly attribute Node firstChild;
     [DeprecateAs=AttrChildAccess] readonly attribute Node lastChild;
 };