Playback rate on MediaPlayer

Add support for modifying the playback rate of a MediaPlayer
 by altering the sample rate of its AudioTrack.
The playback rate is expressed in permille, where 1000 is the
 playback at normal speed.

Change-Id: I981d060ab32f7bae7a767e82c60c88ae635dceed
diff --git a/include/media/MediaPlayerInterface.h b/include/media/MediaPlayerInterface.h
index 7beb176..77c82b2 100644
--- a/include/media/MediaPlayerInterface.h
+++ b/include/media/MediaPlayerInterface.h
@@ -96,6 +96,8 @@
         virtual void        flush() = 0;
         virtual void        pause() = 0;
         virtual void        close() = 0;
+
+        virtual status_t    setPlaybackRatePermille(int32_t rate) { return INVALID_OPERATION; }
     };
 
                         MediaPlayerBase() : mCookie(0), mNotify(0) {}