Enable FastTrack timestamps

Bug: 26413951
Change-Id: Id54c32cb0f0be83d443f6cf1007181ebc461c586
diff --git a/services/audioflinger/PlaybackTracks.h b/services/audioflinger/PlaybackTracks.h
index c81bbf9..fe3cc53 100644
--- a/services/audioflinger/PlaybackTracks.h
+++ b/services/audioflinger/PlaybackTracks.h
@@ -89,6 +89,7 @@
     // ExtendedAudioBufferProvider interface
     virtual size_t framesReady() const;
     virtual size_t framesReleased() const;
+    virtual void onTimestamp(const AudioTimestamp &timestamp);
 
     bool isPausing() const { return mState == PAUSING; }
     bool isPaused() const { return mState == PAUSED; }