Add support for content hints to VideoTrack.

webrtc/api/videotrack.h

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 18 matching lines @@
       const std::string& label,
       VideoTrackSourceInterface* source);
 
   void AddOrUpdateSink(rtc::VideoSinkInterface<VideoFrame>* sink,
                        const rtc::VideoSinkWants& wants) override;
   void RemoveSink(rtc::VideoSinkInterface<VideoFrame>* sink) override;
 
   VideoTrackSourceInterface* GetSource() const override {
     return video_source_.get();
   }
+  ContentHint content_hint() const override;
+  void set_content_hint(ContentHint hint) override;
   bool set_enabled(bool enable) override;
   std::string kind() const override;
 
  protected:
   VideoTrack(const std::string& id, VideoTrackSourceInterface* video_source);
   ~VideoTrack();
 
  private:
   // Implements ObserverInterface. Observes |video_source_| state.
   void OnChanged() override;
 
   rtc::ThreadChecker signaling_thread_checker_;
   rtc::ThreadChecker worker_thread_checker_;
   rtc::scoped_refptr<VideoTrackSourceInterface> video_source_;
+  ContentHint content_hint_ GUARDED_BY(signaling_thread_checker_);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_VIDEOTRACK_H_