IDL: make optional arguments (without default) explicit sometimes

Source/core/plugins/MimeTypeArray.idl

 /*
     Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
     Copyright (C) 2008 Apple Inc. 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.
 
     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.
 */
 
 [
     WillBeGarbageCollected,
     ImplementedAs=DOMMimeTypeArray
 ] interface MimeTypeArray {
     readonly attribute unsigned long length;
-    getter MimeType item([Default=Undefined] optional unsigned long index);
-    MimeType namedItem([Default=Undefined] optional DOMString name);
-    [NotEnumerable, ImplementedAs=namedItem] getter MimeType ([Default=Undefined] optional DOMString name);
+    getter MimeType item(optional unsigned long index);
+    MimeType namedItem(optional DOMString name);
+    [NotEnumerable, ImplementedAs=namedItem] getter MimeType (optional DOMString name);
 };