Now that I'm farther along in the code, I'm wondering if this is strictly necessary. We're consistently using `message.data.type` in the handlers:

https://github.com/oconnore/gaia/blob/0b227d715a82c6f10442b1b28e400ab1e0403b2e/apps/clock/js/active_alarm.js#L114
https://github.com/oconnore/gaia/blob/0b227d715a82c6f10442b1b28e400ab1e0403b2e/apps/clock/js/active_alarm.js#L187

In what contexts will we need to use `message.type`?