IDL: make optional arguments (without default) explicit sometimes

Source/core/events/CompositionEvent.idl

 /*
  * Copyright (C) 2009 Apple Inc. 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 15 matching lines @@
 [
     EventConstructor,
 ] interface CompositionEvent : UIEvent {
 
     [InitializedByEventConstructor] readonly attribute DOMString data;
 
     [RuntimeEnabled=IMEAPI] readonly attribute long activeSegmentStart;
     [RuntimeEnabled=IMEAPI] readonly attribute long activeSegmentEnd;
     [RuntimeEnabled=IMEAPI] sequence<unsigned long> getSegments();
 
-    void initCompositionEvent([Default=Undefined] optional DOMString typeArg,
-                              [Default=Undefined] optional boolean canBubbleArg,
-                              [Default=Undefined] optional boolean cancelableArg,
-                              [Default=Undefined] optional Window viewArg,
-                              [Default=Undefined] optional DOMString dataArg);
+    void initCompositionEvent(optional DOMString typeArg,
+                              optional boolean canBubbleArg,
+                              optional boolean cancelableArg,
+                              optional Window viewArg,
+                              optional DOMString dataArg);
 
 };