After installing a fresh 14.04 install and then installing google-chrome-unstable (Version 36.0.1933.0 dev aura) from the google repository, neither the google chrome icon nor the 'Google Now' notification bell icon appear on the notification bar.
In all my previous installs it would appear as soon as I launched Chrome for the first time after installing. I've naturally tried rebooting, reinstalling and making sure the "Continue running background apps when Google Chrome is closed" setting enabled.
Edit: After installing Dropbox I noticed its tray icon isn't showing either, so I figured it was a global issue rather than chrome-specific. Eventually found the solution below (see answer).