Comment 7 for bug 915253

This should be doable just within indicator-sound these days. The greeter shares which user is selected over DBus. And indicator-sound can register a custom field with AccountsService by itself.

See https://code.launchpad.net/~mterry/telephony-service/greeter-contacts/+merge/199910 for an example of adding a new field and listening for greeter user changes (though granted, that's qt code instead of glib.

This has become more important with the phablet images, since once we split the greeter, the user will definitely have the expectation that volume changes in greeter will carry over.