Support indexed setter generation

Source/bindings/tests/idls/TestEventTarget.idl

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary formstrArg, 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 15 matching lines @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     EventTarget,
     MasqueradesAsUndefined
 ] interface TestEventTarget {
 
     getter Node item([IsIndex] unsigned long index);
     getter Node namedItem(DOMString name);
-    [ImplementedAs=anonymousNamedSetter] setter Node(DOMString name, DOMString value);
+    [ImplementedAs=anonymousNamedSetter] setter Node(DOMString name, [TreatUndefinedAs=anonymousNamedSetterUndefined] DOMString value);
     [ImplementedAs=anonymousIndexedDeleter, RaisesException] deleter boolean(unsigned long index);
     [ImplementedAs=anonymousNamedDeleter] deleter boolean(DOMString name);
 
     void addEventListener(DOMString type, 
                           EventListener listener, 
                           optional boolean useCapture);
     void removeEventListener(DOMString type, 
                              EventListener listener, 
                              optional boolean useCapture);
     [RaisesException] boolean dispatchEvent(Event evt);
 };