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

media/audio/null_audio_sink.cc

Index: media/audio/null_audio_sink.cc
diff --git a/media/audio/null_audio_sink.cc b/media/audio/null_audio_sink.cc
index 6d40c93e2b67a28a71aaf7840977a6258408972f..15ff18b7483ec482f975252e3d75e759105ac9e9 100644
--- a/media/audio/null_audio_sink.cc
+++ b/media/audio/null_audio_sink.cc
@@ -79,6 +79,10 @@ OutputDeviceInfo NullAudioSink::GetOutputDeviceInfo() {
   return OutputDeviceInfo();
 }
 
+bool NullAudioSink::BelongsToRenderingThread() {
+  return task_runner_->BelongsToCurrentThread();
+}
+
 void NullAudioSink::SwitchOutputDevice(const std::string& device_id,
                                        const url::Origin& security_origin,
                                        const OutputDeviceStatusCB& callback) {