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 cc65aabcd59700ebbdd2f7a4b5a81e39a637dc43..f11f72e6618b5c4449f7b75507c93f07af92c38d 100644
--- a/webrtc/media/base/fakemediaengine.h
+++ b/webrtc/media/base/fakemediaengine.h
@@ -682,6 +682,7 @@ class FakeVoiceEngine : public FakeBaseEngine {
   }
 
   VoiceMediaChannel* CreateChannel(webrtc::Call* call,
+                                   const webrtc::MediaConfig& config,
                                    const AudioOptions& options) {
     if (fail_create_channel_) {
       return nullptr;
@@ -745,6 +746,7 @@ class FakeVideoEngine : public FakeBaseEngine {
   }
 
   VideoMediaChannel* CreateChannel(webrtc::Call* call,
+                                   const webrtc::MediaConfig& config,
                                    const VideoOptions& options) {
     if (fail_create_channel_) {
       return NULL;