google/traceur-compiler — pull request #967 by Alxandr (2014-04-22 00:40:44+00:00)
Title: Added Sets and updated Map to include itterators

According to
http://wiki.ecmascript.org/doku.php?id=harmony:simple_maps_and_sets,
maps should have items, keys and values itterators. Also, added a Set
class.