Greyson Parrelli bf692e8da3 Throttle background contact syncs to once every 6 hours.
Unfortunately, there's apps out there that trigger contact changes
very frequently. Because we listen to the system for contact
changes to tell us when to sync, that could result in us sending
an abundance of contact syncs to linked desktop instances.

This throttles contact sync requests using the following methodology:

- By default, throttle contact syncs to 6 hrs while the app is
  backgrounded.
- If a sync is throttled in the background, we set a dirty flag and
  will execute the sync the next time the app is foregrounded.
- Syncs explicitly requested by desktop are never throttled.
2018-07-17 12:06:50 -07:00
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