Adding "adapter" ORTC objects on top of ChannelManager/BaseChannel/etc.

webrtc/pc/mediasession.h

Index: webrtc/pc/mediasession.h
diff --git a/webrtc/pc/mediasession.h b/webrtc/pc/mediasession.h
index 68f4c370994eb7b44a3aae29da263f2c8e60dd24..3b4340c299e85bc82c439abd89fdd5f55e9a89b2 100644
--- a/webrtc/pc/mediasession.h
+++ b/webrtc/pc/mediasession.h
@@ -92,6 +92,10 @@ struct RtpTransceiverDirection {
       MediaContentDirection md);
 
   MediaContentDirection ToMediaContentDirection() const;
+
+  RtpTransceiverDirection Reversed() const {
+    return RtpTransceiverDirection(recv, send);
+  }
 };
 
 RtpTransceiverDirection