These will be useful to keep track of changes across different places in the new UI. https://bugzilla.gnome.org/show_bug.cgi?id=785949
New Mutter GetCurrentState now provides a list of available scales, we need to use these values in order to define an UI that shows them all.
This allows us to keep the panel working with GnomeRR while the new mutter api develops. https://bugzilla.gnome.org/show_bug.cgi?id=782785