Refactor VideoTracks to forward all sinks to its source

webrtc/media/base/videosourcebase.h

 /*
  *  Copyright (c) 2016 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 WEBRTC_MEDIA_BASE_VIDEOSOURCEBASE_H_
 #define WEBRTC_MEDIA_BASE_VIDEOSOURCEBASE_H_
 
-// TODO(perkj): Add implementation.
+#include <vector>
+
+#include "webrtc/base/thread_checker.h"
+#include "webrtc/media/base/videoframe.h"
+#include "webrtc/media/base/videosourceinterface.h"
+
+namespace rtc {
+
+// VideoSourceBase is not thread safe.
+class VideoSourceBase : public VideoSourceInterface<cricket::VideoFrame> {
+ public:
+  VideoSourceBase();
+  void AddOrUpdateSink(VideoSinkInterface<cricket::VideoFrame>* sink,
+                       const VideoSinkWants& wants) override;
+  void RemoveSink(VideoSinkInterface<cricket::VideoFrame>* sink) override;
+
+ protected:
+  struct SinkPair {
+    SinkPair(VideoSinkInterface<cricket::VideoFrame>* sink,
+             VideoSinkWants wants)
+        : sink(sink), wants(wants) {}
+    VideoSinkInterface<cricket::VideoFrame>* sink;
+    VideoSinkWants wants;
+  };
+  SinkPair* FindSinkPair(const VideoSinkInterface<cricket::VideoFrame>* sink);
+
+  const std::vector<SinkPair>& sink_pairs() const { return sinks_; }
+  ThreadChecker thread_checker_;
+
+ private:
+  std::vector<SinkPair> sinks_;
+};
+
+}  // namespace rtc
 
 #endif  // WEBRTC_MEDIA_BASE_VIDEOSOURCEBASE_H_