Introduce struct MediaConfig, with construction-time settings.

webrtc/media/webrtc/nullwebrtcvideoengine.h

Index: webrtc/media/webrtc/nullwebrtcvideoengine.h
diff --git a/webrtc/media/webrtc/nullwebrtcvideoengine.h b/webrtc/media/webrtc/nullwebrtcvideoengine.h
index 4f9d2d9c6de19911c2b80039f04c46c56b7ec902..14bae3d56005b8f4f5c65ed1a10357ba1aae569a 100644
--- a/webrtc/media/webrtc/nullwebrtcvideoengine.h
+++ b/webrtc/media/webrtc/nullwebrtcvideoengine.h
@@ -36,7 +36,7 @@
 namespace webrtc {
 
 class Call;
-
+struct MediaConfig;
 }  // namespace webrtc
 
 
@@ -68,6 +68,7 @@ class NullWebRtcVideoEngine {
   }
 
   VideoMediaChannel* CreateChannel(webrtc::Call* call,
+      const webrtc::MediaConfig& config,
       const VideoOptions& options) {
     return nullptr;
   }