Implement op changes for PREDISMISSED_STATE alarms.

Bug: 21492917

Schedule a state change from PREDISMISSED_STATE to DISMISS_STATE at
the original firing time for the alarm.
Add rescheduling behavior for PREDIMISSED alarms; if TIME_SET lands
in the appropriate window, stay PREDISMISSED; otherwise, reschedule
alarm for proper next firing instance.

Change-Id: I3856bac5bb1d4774a3a5284c12b320a2ac3debbe