Introduce struct MediaConfig, with construction-time settings.

webrtc/media/engine/nullwebrtcvideoengine.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.
  */
 
@@ skipping 33 matching lines @@
   const std::vector<VideoCodec>& codecs() {
     return codecs_;
   }
 
   RtpCapabilities GetCapabilities() {
     RtpCapabilities capabilities;
     return capabilities;
   }
 
   VideoMediaChannel* CreateChannel(webrtc::Call* call,
-      const VideoOptions& options) {
+                                   const MediaConfig& config,
+                                   const VideoOptions& options) {
     return nullptr;
   }
 
  private:
   std::vector<VideoCodec> codecs_;
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_MEDIA_ENGINE_NULLWEBRTCVIDEOENGINE_H_