Fix issue 3157123.

Use a Mutex wherever atomic operations were used in AudioTrack,
AudioRecord, AudioFlinger and AudioEffect classes.

Change-Id: I6f55b2cabdcd93d64ef19446735b8f33720f8dbc
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 4475d4a..813a905 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -480,6 +480,7 @@
     uint32_t                mFlags;
     int                     mSessionId;
     int                     mAuxEffectId;
+    Mutex                   mLock;
 };