AudioTrack::dump() comment

Change-Id: Id3b5210293a77404189555a0c797fb099e3c6c04
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 1d99c86..0094ff0 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -584,6 +584,7 @@
 
     /*
      * Dumps the state of an audio track.
+     * Not a general-purpose API; intended only for use by media player service to dump its tracks.
      */
             status_t    dump(int fd, const Vector<String16>& args) const;