Avoid hitting the thread check when WebRtcAudioRenderer is going away.

content/renderer/media/media_stream_audio_processor.cc

Index: content/renderer/media/media_stream_audio_processor.cc
diff --git a/content/renderer/media/media_stream_audio_processor.cc b/content/renderer/media/media_stream_audio_processor.cc
index fc61c3f2b7c7e3b6cc0aad0b67830812c5583cab..720afbf5e54306e641eb207f1d6d0616410599b5 100644
--- a/content/renderer/media/media_stream_audio_processor.cc
+++ b/content/renderer/media/media_stream_audio_processor.cc
@@ -218,6 +218,14 @@ void MediaStreamAudioProcessor::OnPlayoutData(media::AudioBus* audio_bus,
     audio_processing_->AnalyzeReverseStream(&render_frame_);
 }
 
+void MediaStreamAudioProcessor::OnPlayoutDataSourceChanged() {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  // There is no need to hold a lock here since the caller guarantees that
+  // there is no more OnPlayoutData() callback on the render thread.
+  render_thread_checker_.DetachFromThread();
+  render_converter_.reset();
+}
+
 void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
     const blink::WebMediaConstraints& constraints, int effects) {
   DCHECK(!audio_processing_);