Add support for content hints to VideoTrack.

webrtc/api/videotrack.cc

Index: webrtc/api/videotrack.cc
diff --git a/webrtc/api/videotrack.cc b/webrtc/api/videotrack.cc
index b47a32044f33d4ee7f0e52bf41016076a5fb4b3b..2fa2ba671a8724b3f8a6fff3fa5b1015b2a15bf2 100644
--- a/webrtc/api/videotrack.cc
+++ b/webrtc/api/videotrack.cc
@@ -19,7 +19,8 @@ const char MediaStreamTrackInterface::kVideoKind[] = "video";
 VideoTrack::VideoTrack(const std::string& label,
                        VideoTrackSourceInterface* video_source)
     : MediaStreamTrack<VideoTrackInterface>(label),
-      video_source_(video_source) {
+      video_source_(video_source),
+      content_hint_(ContentHint::kNone) {
   worker_thread_checker_.DetachFromThread();
   video_source_->RegisterObserver(this);
 }
@@ -49,6 +50,19 @@ void VideoTrack::RemoveSink(rtc::VideoSinkInterface<VideoFrame>* sink) {
   video_source_->RemoveSink(sink);
 }
 
+VideoTrackInterface::ContentHint VideoTrack::content_hint() const {
+  RTC_DCHECK_RUN_ON(&signaling_thread_checker_);
+  return content_hint_;
+}
+
+void VideoTrack::set_content_hint(ContentHint hint) {
+  RTC_DCHECK_RUN_ON(&signaling_thread_checker_);
+  if (content_hint_ == hint)
+    return;
+  content_hint_ = hint;
+  Notifier<VideoTrackInterface>::FireOnChanged();
+}
+
 bool VideoTrack::set_enabled(bool enable) {
   RTC_DCHECK(signaling_thread_checker_.CalledOnValidThread());
   for (auto& sink_pair : sink_pairs()) {