Make AudioTrack a RefBase so wrappers not needed

Change-Id: I2305abe586ac41251af04a194bc818c110a1b293
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index d1a8105..911a535 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -38,7 +38,7 @@
 
 // ----------------------------------------------------------------------------
 
-class AudioTrack
+class AudioTrack : virtual public RefBase
 {
 public:
     enum channel_index {