core-list in paper-action-dialog doesn't fire activate event

[jakemac53]

see original report https://groups.google.com/a/dartlang.org/forum/?utm_medium=email&utm_source=footer#!msg/web/wM3diTT5Ceg/98pfjFUs6wQJ.

dart repro: https://gist.github.com/jakemac53/8a4e59c61acbeb80d1cc

js clone which works: http://jsbin.com/giregemanu/1/edit