Introduce struct MediaConfig, with construction-time settings.

webrtc/media/base/fakemediaengine.h

Index: webrtc/media/base/fakemediaengine.h
diff --git a/webrtc/media/base/fakemediaengine.h b/webrtc/media/base/fakemediaengine.h
index 49790cb053531525d6260c60c8e3287cdc1b51ac..f2de5ac6538fc3bc68689bb60b66ff9258b467c2 100644
--- a/webrtc/media/base/fakemediaengine.h
+++ b/webrtc/media/base/fakemediaengine.h
@@ -665,6 +665,7 @@ class FakeVoiceEngine : public FakeBaseEngine {
   }
 
   VoiceMediaChannel* CreateChannel(webrtc::Call* call,
+                                   const MediaConfig& config,
                                    const AudioOptions& options) {
     if (fail_create_channel_) {
       return nullptr;
@@ -728,6 +729,7 @@ class FakeVideoEngine : public FakeBaseEngine {
   }
 
   VideoMediaChannel* CreateChannel(webrtc::Call* call,
+                                   const MediaConfig& config,
                                    const VideoOptions& options) {
     if (fail_create_channel_) {
       return NULL;