[Chromecast] Allow CMA backend to notify of key expiry

chromecast/media/audio/cast_audio_output_stream.cc

Index: chromecast/media/audio/cast_audio_output_stream.cc
diff --git a/chromecast/media/audio/cast_audio_output_stream.cc b/chromecast/media/audio/cast_audio_output_stream.cc
index 98aae108c23c2f754579606e8e7f760ab0143114..3d1419aed9e908804e1d16556a425f01897acf8b 100644
--- a/chromecast/media/audio/cast_audio_output_stream.cc
+++ b/chromecast/media/audio/cast_audio_output_stream.cc
@@ -175,6 +175,10 @@ class CastAudioOutputStream::Backend : public MediaPipelineBackend::Delegate {
       OnPushBufferComplete(decoder_, MediaPipelineBackend::kBufferFailed);
   }
 
+  void OnKeyStatusChanged(const std::string& key_id,
+                          CastKeyStatus key_status,
+                          uint32_t system_code) override {}
+
   base::WeakPtr<CastAudioOutputStream::Backend> GetWeakPtr() {
     return weak_factory_.GetWeakPtr();
   }