IDL: make optional arguments (without default) explicit sometimes

Source/core/frame/WindowTimers.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 20 matching lines @@
     ImplementedAs=DOMWindowTimers,
     LegacyTreatAsPartialInterface,
     NoInterfaceObject, // Always used on target of 'implements'
 ] interface WindowTimers {
     // FIXME: currently using [Custom] and |any| because overload algorithm
     // can't handle Function/DOMString overload properly
     // http://crbug.com/293561
     // FIXME: would be clearer as a union type, like:
     // typedef (Function or DOMString) Handler
     // Needs spec update and better union support: http://crbug.com/240176
-    [Custom] long setTimeout(any handler, [Default=Undefined] optional long timeout);
-    void clearTimeout([Default=Undefined] optional long handle);
-    [Custom] long setInterval(any handler, [Default=Undefined] optional long timeout);
-    void clearInterval([Default=Undefined] optional long handle);
+    [Custom] long setTimeout(any handler, optional long timeout);
+    void clearTimeout(optional long handle);
+    [Custom] long setInterval(any handler, optional long timeout);
+    void clearInterval(optional long handle);
 };