[Chromecast] Fade in after a mixer input stream has skipped

chromecast/media/cma/backend/alsa/stream_mixer_alsa.h

Index: chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
diff --git a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
index e189d1db2749209a1511c4b2bea9bd56c351985e..c26c10e39bbb50f6119f6f20ab9b8bb8ba740cb4 100644
--- a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
+++ b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
@@ -93,6 +93,11 @@ class StreamMixerAlsa {
     // MaxReadSize(), and |dest->frames()| shall be >= |frames|.
     virtual void GetResampledData(::media::AudioBus* dest, int frames) = 0;
 
+    // Called when this input has been skipped for output due to not having any
+    // data available. This indicates that there will be a gap in the playback
+    // from this stream.
+    virtual void OnSkipped() = 0;
+
     // This is called for every InputQueue when the mixer writes data to ALSA
     // for any of its input streams.
     virtual void AfterWriteFrames(