Lock SyncQueue when user starting, copy RSC list.

Document SyncQueue locking policy and protect in onUserStarting()
and clearAllBackoffs().  Return copy of ServiceInfo list from
RegisteredServicesCache instead of exposing locking externally.

Bug: 7357776, 7352537
Change-Id: I6a32ca98a355b639d4207a88bde572179beae359
4 files changed