IDL: make optional arguments (without default) explicit sometimes

Source/core/events/CustomEvent.idl

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 10 matching lines @@
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     EventConstructor,
 ] interface CustomEvent : Event {
     [Custom=Getter, InitializedByEventConstructor] readonly attribute any detail;
 
-    [Custom] void initCustomEvent([Default=Undefined] optional DOMString typeArg,
-                                  [Default=Undefined] optional boolean canBubbleArg,
-                                  [Default=Undefined] optional boolean cancelableArg,
-                                  [Default=Undefined] optional any detailArg);
+    [Custom] void initCustomEvent(optional DOMString typeArg,
+                                  optional boolean canBubbleArg,
+                                  optional boolean cancelableArg,
+                                  optional any detailArg);
 };