Interface for media transport

This is experimental interface for media transport.

The goal is to refactor WebRTC codebase to send/receive frames via media transport interface. It will allow us to have different media transport implementations in the future, including QUIC-based media transport.

Bug: webrtc:9719
Change-Id: I64e0b69d18c212e1ed0a08c6904578c3dfbe3af7
Reviewed-on: https://webrtc-review.googlesource.com/95960
Commit-Queue: Anton Sukhanov <sukhanov@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Bjorn Mellem <mellem@webrtc.org>
Reviewed-by: Peter Slatala <psla@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24612}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index b6ad1d6..c5c5713 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -63,6 +63,7 @@
     "jsepicecandidate.cc",
     "jsepicecandidate.h",
     "jsepsessiondescription.h",
+    "media_transport_interface.h",
     "mediaconstraintsinterface.cc",
     "mediaconstraintsinterface.h",
     "mediastreaminterface.cc",