* Followup to 85d765f4
* Workaround for (HTC bug: 2275383) & (Moto bug: 2226582)
* Restores mSyncKey as null instead of empty string, which is how
a new account is initialized. Bug: 2385980
* Cleanup synchronized logic in backup & restore
* Minor cleanups & improved comments
Cherry-picked from master d612717340
346a0cc1e0