Introduce struct MediaConfig, with construction-time settings.

talk/session/media/channelmanager.cc

Index: talk/session/media/channelmanager.cc
diff --git a/talk/session/media/channelmanager.cc b/talk/session/media/channelmanager.cc
index 9cac1451a297611a88468393a89976f907a80061..23a9651643073ad40154f53ba539fc8c99c04c87 100644
--- a/talk/session/media/channelmanager.cc
+++ b/talk/session/media/channelmanager.cc
@@ -266,8 +266,8 @@ VoiceChannel* ChannelManager::CreateVoiceChannel_w(
   ASSERT(initialized_);
   ASSERT(worker_thread_ == rtc::Thread::Current());
   ASSERT(nullptr != media_controller);
-  VoiceMediaChannel* media_channel =
-      media_engine_->CreateChannel(media_controller->call_w(), options);
+  VoiceMediaChannel* media_channel = media_engine_->CreateChannel(
+      media_controller->call_w(), media_controller->config(), options);
   if (!media_channel)
     return nullptr;
 
@@ -324,8 +324,8 @@ VideoChannel* ChannelManager::CreateVideoChannel_w(
   ASSERT(initialized_);
   ASSERT(worker_thread_ == rtc::Thread::Current());
   ASSERT(nullptr != media_controller);
-  VideoMediaChannel* media_channel =
-      media_engine_->CreateVideoChannel(media_controller->call_w(), options);
+  VideoMediaChannel* media_channel = media_engine_->CreateVideoChannel(
+      media_controller->call_w(), media_controller->config(), options);
   if (media_channel == NULL) {
     return NULL;
   }