Comment 13 for bug 1679528

It's probably worth noting that at least Chrome seems to have been fixed to work with the system default of "XDG_CURRENT_DESKTOP=Unity:Unity7". That is, the original complaint of not being able to see Chrome/Hangouts icons in the notification tray is not an issue (don't know about Skype). However, I suspect there are still a lot of packages out there that have not been updated (and hence only work when the value is "Unity").

I know for sure that at least Slack 2.6.3 still does not show a tray icon without the aforementioned fix.