mediaplayer: support dynamic playback rate

Bug: 19196501

Change-Id: I856b1507d5fa2cedfb645706d2435683a7d3e050
diff --git a/include/media/mediaplayer.h b/include/media/mediaplayer.h
index 5830933..808e893 100644
--- a/include/media/mediaplayer.h
+++ b/include/media/mediaplayer.h
@@ -220,6 +220,7 @@
             status_t        stop();
             status_t        pause();
             bool            isPlaying();
+            status_t        setPlaybackRate(float rate);
             status_t        getVideoWidth(int *w);
             status_t        getVideoHeight(int *h);
             status_t        seekTo(int msec);
@@ -274,6 +275,7 @@
     int                         mVideoWidth;
     int                         mVideoHeight;
     int                         mAudioSessionId;
+    float                       mPlaybackRate;
     float                       mSendLevel;
     struct sockaddr_in          mRetransmitEndpoint;
     bool                        mRetransmitEndpointValid;