Stub out indexed setter for HTMLOptionsCollection.

Source/WebCore/bindings/dart/custom/DartHTMLOptionsCollectionCustom.cpp

 // Copyright 2011, 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:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
     // FIXME: proper implementation.
     DART_UNIMPLEMENTED();
 }
 
 void lengthSetter(Dart_NativeArguments)
 {
     // FIXME: proper implementation.
     DART_UNIMPLEMENTED();
 }
 
+void numericIndexSetterCallback(Dart_NativeArguments)
+{
+    // FIXME: proper implementation.
+    DART_UNIMPLEMENTED();
+}
+
 }
 
 }