Call method while holding lock.

The method removeRecentTasksForUser() was being called without the
ActivityManagerService lock held. This change calles it while the
lock is held and renames it to indicate that it should be called
while holding the lock.

Fixes bug 16775111.

Change-Id: I002f9f96d407de458934da8bc728acd54f0c398c
1 file changed