Change audio render thread checking to use new AudioRendererSink::BelongsToRendererThread()

media/audio/null_audio_sink.h

Index: media/audio/null_audio_sink.h
diff --git a/media/audio/null_audio_sink.h b/media/audio/null_audio_sink.h
index 6d24fbe39c6c81ccf2a3e835a8d38c092e9c4f28..e9acd6c9e9c787bdbc0e9c9585abed77b9d32742 100644
--- a/media/audio/null_audio_sink.h
+++ b/media/audio/null_audio_sink.h
@@ -34,6 +34,7 @@ class MEDIA_EXPORT NullAudioSink
   void Play() override;
   bool SetVolume(double volume) override;
   OutputDeviceInfo GetOutputDeviceInfo() override;
+  bool BelongsToRenderingThread() override;
   void SwitchOutputDevice(const std::string& device_id,
                           const url::Origin& security_origin,
                           const OutputDeviceStatusCB& callback) override;