Clarification around data.days entries

[Brendan Colloran]

A few of us have been discussing how data.days works, and we want to be sure we understand it correctly and that we've given everyone an opportunity to flag any potential nuances in the behavior. GPS and rnewman (or whoever gets there first) can you confirm for desktop and Fennec respectively that:

* Any calendar day on which an instance is active will have an entry in data.days, even if the activity is from a sessions that started many days ago?
* If there is no new data for a particular day (i.e., no new bookmarks, no searches, no environment changes of any sort), what is the required set of entries that will always be included for all days (addons.counts, places.places, appInfo.appinfo, etc?)
* The client uses UTC to determine the calendar date on which activity has occurred (ignoring clock skew).
* appSessions is recorded on the date a session starts and only on that date, including long sessions that run across multiple calendar dates.
** These long-running sessions are stored in appSession.current, and only flushed to data.days when the next session starts.

We're basically trying to double-check our understanding the that we can get a accurate count of all the active FF instances on a given date by just counting up all the data.day entries present on that date (orphaning and clock skew aside). If there's any nuance we're missing here, please let us know.

thanks,
brendan