Add ExtendedAudioBufferProvider::framesReleased and onTimestamp

and implement them in SourceAudioBufferProvider using the associated NBAIO_Source,
and in Track using the associated AudioTrackServerProxy.

Change-Id: I60dc4adba63fc1dc452ff16caf347e4a7c8242c2
diff --git a/services/audioflinger/PlaybackTracks.h b/services/audioflinger/PlaybackTracks.h
index d34833f..0308b99 100644
--- a/services/audioflinger/PlaybackTracks.h
+++ b/services/audioflinger/PlaybackTracks.h
@@ -81,7 +81,9 @@
                                    int64_t pts = kInvalidPTS);
     // releaseBuffer() not overridden
 
+    // ExtendedAudioBufferProvider interface
     virtual size_t framesReady() const;
+    virtual size_t framesReleased() const;
 
     bool isPausing() const { return mState == PAUSING; }
     bool isPaused() const { return mState == PAUSED; }