mediaplayer: support dynamic playback rate

Bug: 19196501

Change-Id: I856b1507d5fa2cedfb645706d2435683a7d3e050
diff --git a/media/libmediaplayerservice/MediaPlayerService.h b/media/libmediaplayerservice/MediaPlayerService.h
index fad3447..7320311 100644
--- a/media/libmediaplayerservice/MediaPlayerService.h
+++ b/media/libmediaplayerservice/MediaPlayerService.h
@@ -261,6 +261,7 @@
         virtual status_t        stop();
         virtual status_t        pause();
         virtual status_t        isPlaying(bool* state);
+        virtual status_t        setPlaybackRate(float rate);
         virtual status_t        seekTo(int msec);
         virtual status_t        getCurrentPosition(int* msec);
         virtual status_t        getDuration(int* msec);