Bug 958900 - Pre: correct comment.
Bug 958900 - Pre: fix JavaDoc.
Bug 958900 - Part 1: extract (Prefs)BackoffHandler from Sync 1.1 SyncAdapter.
Bug 958900 - Part 2: rename shouldBackOff to shouldBackOffStorage.
Bug 958900 - Part 3: add SchedulePolicy interface for adjusting how FxAccountSyncAdapter will sync.
Bug 958900 - Part 4: implement backoff and periodic sync scheduling for FxAccountSyncAdapter.
Review comment: add Javadoc for BaseGlobalSessionCallback#shouldBackOffStorage.
Review comment: remove abstract from interface.
Review comment: simplify PrefsBackoffHandler constructor, standardize on implicit leading dot in PrefsBackoffHandler path.
Review comment: remove redundant comment.
Review comment: note about efficiency of polling for verification.
Review comment: move DefaultSchedulePolicy constructor.
Review comment: belt-and-braces range checking in postponeSync.
Review comment: explanation for configureBackoff methods.
Review comment: extract DefaultSchedulePolicy => FxAccountSchedulePolicy.
Review comment: call handleSuccess on a successful sync.
Review comment: lift shouldSync into the SyncAdapters.