services If the SelectPrinterActivity is visible it shows different emptyState depending on if there are print services available or not. Hence the activity has to listen to changes to the list of enabled services. This also fixes a small syncronsation problem if two observers are registered for the enabled print services. Bug: 25666802 Change-Id: I79af66f25f10e66347b48ce9bb99c1657b30a8dd