Add es3 to catch use of 'new' as object key.

This would have caught the IE8 breakage of
  mw.flow.action.topic.new();
that was fixed in 7c7b7c21a.

Change-Id: I6e7ab8de037fb23460fdb13b7bdc83dda093a9ae
Merge "Add es3 to catch use of 'new' as object key."