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diff --git a/third_party/libwebrtc/pc/media_stream_observer.h b/third_party/libwebrtc/pc/media_stream_observer.h
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+++ b/third_party/libwebrtc/pc/media_stream_observer.h
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+/*
+ *  Copyright 2015 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.
+ */
+
+#ifndef PC_MEDIA_STREAM_OBSERVER_H_
+#define PC_MEDIA_STREAM_OBSERVER_H_
+
+#include <functional>
+
+#include "api/media_stream_interface.h"
+#include "api/scoped_refptr.h"
+
+namespace webrtc {
+
+// Helper class which will listen for changes to a stream and emit the
+// corresponding signals.
+class MediaStreamObserver : public ObserverInterface {
+ public:
+  explicit MediaStreamObserver(
+      MediaStreamInterface* stream,
+      std::function<void(AudioTrackInterface*, MediaStreamInterface*)>
+          audio_track_added_callback,
+      std::function<void(AudioTrackInterface*, MediaStreamInterface*)>
+          audio_track_removed_callback,
+      std::function<void(VideoTrackInterface*, MediaStreamInterface*)>
+          video_track_added_callback,
+      std::function<void(VideoTrackInterface*, MediaStreamInterface*)>
+          video_track_removed_callback);
+  ~MediaStreamObserver() override;
+
+  const MediaStreamInterface* stream() const { return stream_.get(); }
+
+  void OnChanged() override;
+
+ private:
+  rtc::scoped_refptr<MediaStreamInterface> stream_;
+  AudioTrackVector cached_audio_tracks_;
+  VideoTrackVector cached_video_tracks_;
+  const std::function<void(AudioTrackInterface*, MediaStreamInterface*)>
+      audio_track_added_callback_;
+  const std::function<void(AudioTrackInterface*, MediaStreamInterface*)>
+      audio_track_removed_callback_;
+  const std::function<void(VideoTrackInterface*, MediaStreamInterface*)>
+      video_track_added_callback_;
+  const std::function<void(VideoTrackInterface*, MediaStreamInterface*)>
+      video_track_removed_callback_;
+};
+
+}  // namespace webrtc
+
+#endif  // PC_MEDIA_STREAM_OBSERVER_H_