Respond to route changes via mct-before-unload, in order to
show a prompt to allow the user to confirm navigation changes
which do not trigger onbeforeunload (such as using back to
change the hash route). WTD-1035.
Add directive for exposing expressions which should be
evaluated for the browser's onbeforeunload event, to
prevent user-initiated navigation from causing a loss
of unsaved changes. WTD-1035.
