Implement MediaStreamTrack contentHint skeleton.

content/renderer/media/media_stream_audio_track.cc

Index: content/renderer/media/media_stream_audio_track.cc
diff --git a/content/renderer/media/media_stream_audio_track.cc b/content/renderer/media/media_stream_audio_track.cc
index b6ec78e871f093ea072559f22843d8bf146d9173..cb64f8af18db392cdee6789560a9c5e0659857c3 100644
--- a/content/renderer/media/media_stream_audio_track.cc
+++ b/content/renderer/media/media_stream_audio_track.cc
@@ -78,6 +78,16 @@ void MediaStreamAudioTrack::SetEnabled(bool enabled) {
     sink->OnEnabledChanged(enabled);
 }
 
+void MediaStreamAudioTrack::SetContentHint(
+    blink::WebMediaStreamTrack::ContentHintType content_hint) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  std::vector<MediaStreamAudioSink*> sinks_to_notify;
+  deliverer_.GetConsumerList(&sinks_to_notify);
+  for (MediaStreamAudioSink* sink : sinks_to_notify)
+    sink->OnContentHintChanged(content_hint);
+}
+
 void* MediaStreamAudioTrack::GetClassIdentifier() const {
   return nullptr;
 }