Fix bug 4109988 fix deadlock on destroy

Fix bug 4109988 fix deadlock on destroy

Fix deadlock with an AudioPlayer playing from a PCM buffer queue.
This type of player uses an AudioTrack that pulls data through
 its callback from a buffer queue.
This issue is that when you destroy the player (whick locks the
 object), it tries to destroy the AudioTrack object. The
 AudioTrack destructor can only finish when the AudioTrack
 callback thread can exit. If a callback was underway when
 trying to destroy the object, a race condition existed for
 the AudioPlayer lock.
The fix consists in using the "pre-destroy" hook for the AudioPlayer
 object. In it, we unlock the AudioPlayer, and block until the
 AudioTrack callback has signaled it's done. The pre-destroy
 hook also marks the track as "about to be destroyed" so any
 callback that gets called once the pre-destroy hook has been
 called can return immediately.

Change-Id: I4ca69157ff381232c1edc8fb576c6d9e90c2777f