Fix batterySendBroadcast not synchronized issue.

Symptom: system server crash.
Root Cause: batterySendBroadcast not sychrnized with AMS object,
caused system crash in broadcastIntentLocked()
when 2 threads access mParallelBroadcasts.get(i).intent but get null
in BroadcastQueue.replaceParallelBroadcastLocked().
Solution: add sychronization object.

Change-Id: I99f751a2cd3e6fa1dbe2812f5f129525013d6a7f