IDL: make optional arguments (without default) explicit sometimes

Source/modules/indexeddb/IDBCursor.idl

 /*
  * Copyright (C) 2010 Google 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
@@ skipping 25 matching lines @@
     GarbageCollected
 ] interface IDBCursor {
 
     readonly attribute IDBCursorDirection direction;
     [CallWith=ScriptState, CachedAttribute=isKeyDirty] readonly attribute any key;
     [CallWith=ScriptState, CachedAttribute=isPrimaryKeyDirty] readonly attribute any primaryKey;
     [CallWith=ScriptState] readonly attribute any source;
 
     [CallWith=ScriptState, RaisesException] IDBRequest update(any value);
     [RaisesException] void advance([EnforceRange] unsigned long count);
-    [CallWith=ScriptState, ImplementedAs=continueFunction, RaisesException] void continue([Default=Undefined] optional any key);
+    [CallWith=ScriptState, ImplementedAs=continueFunction, RaisesException] void continue(optional any key);
     [CallWith=ScriptState, RaisesException, RuntimeEnabled=IndexedDBExperimental] void continuePrimaryKey(any key, any primaryKey);
     [CallWith=ScriptState, ImplementedAs=deleteFunction, RaisesException] IDBRequest delete();
 };