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..06f57ccfd47022104e45bec253f2fbd5007dfbd0 100644
--- a/talk/session/media/channelmanager.cc
+++ b/talk/session/media/channelmanager.cc
@@ -267,7 +267,9 @@ VoiceChannel* ChannelManager::CreateVoiceChannel_w(
   ASSERT(worker_thread_ == rtc::Thread::Current());
   ASSERT(nullptr != media_controller);
   VoiceMediaChannel* media_channel =
-      media_engine_->CreateChannel(media_controller->call_w(), options);
+      media_engine_->CreateChannel(media_controller->call_w(),
+                                   media_controller->config(),
+                                   options);
   if (!media_channel)
     return nullptr;
 
@@ -325,7 +327,9 @@ VideoChannel* ChannelManager::CreateVideoChannel_w(
   ASSERT(worker_thread_ == rtc::Thread::Current());
   ASSERT(nullptr != media_controller);
   VideoMediaChannel* media_channel =
-      media_engine_->CreateVideoChannel(media_controller->call_w(), options);
+      media_engine_->CreateVideoChannel(media_controller->call_w(),
+                                        media_controller->config(),
+                                        options);
   if (media_channel == NULL) {
     return NULL;
   }