Add AudioFlinger::PlaybackThread::Track::getTimestamp()

with a dummy implementation initially,
and use it in AudioFlinger::TrackHandle::getTimestamp()

Change-Id: I2da88fc52a135a7f0d9fd9538986e919dc8ccd3b
diff --git a/services/audioflinger/PlaybackTracks.h b/services/audioflinger/PlaybackTracks.h
index 5600411c..d34833f 100644
--- a/services/audioflinger/PlaybackTracks.h
+++ b/services/audioflinger/PlaybackTracks.h
@@ -59,6 +59,7 @@
             void        setMainBuffer(int16_t *buffer) { mMainBuffer = buffer; }
             int16_t     *mainBuffer() const { return mMainBuffer; }
             int         auxEffectId() const { return mAuxEffectId; }
+    virtual status_t    getTimestamp(AudioTimestamp& timestamp);
 
 // implement FastMixerState::VolumeProvider interface
     virtual uint32_t    getVolumeLR();