Introduce struct MediaConfig, with construction-time settings.

talk/app/webrtc/peerconnectionfactory.cc

Index: talk/app/webrtc/peerconnectionfactory.cc
diff --git a/talk/app/webrtc/peerconnectionfactory.cc b/talk/app/webrtc/peerconnectionfactory.cc
index a781eb3e2594240b67aa6e61a01e11fa9b6718e8..205d65b215eddc78db18a0e3337e36cf8880e2a4 100644
--- a/talk/app/webrtc/peerconnectionfactory.cc
+++ b/talk/app/webrtc/peerconnectionfactory.cc
@@ -303,10 +303,11 @@ PeerConnectionFactory::CreateAudioTrack(const std::string& id,
   return AudioTrackProxy::Create(signaling_thread_, track);
 }
 
-webrtc::MediaControllerInterface* PeerConnectionFactory::CreateMediaController()
+webrtc::MediaControllerInterface* PeerConnectionFactory::CreateMediaController(
+    const MediaConfig& config)
     const {
   RTC_DCHECK(signaling_thread_->IsCurrent());
-  return MediaControllerInterface::Create(worker_thread_,
+  return MediaControllerInterface::Create(worker_thread_, config,
                                           channel_manager_.get());
 }