Add SCTP transport to the public API.

This involves inserting an extra layer between jsep_transport_controller
and the cricket::SctpTransportInternal layer. The objects at this layer
are reference counted.

Bug: chromium:818643
Change-Id: Ibed57c4a538de981cee63e0f7f1f319f029cab39
Reviewed-on: https://webrtc-review.googlesource.com/c/123884
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26889}
diff --git a/pc/jsep_transport_controller_unittest.cc b/pc/jsep_transport_controller_unittest.cc
index 590f57d..4375080 100644
--- a/pc/jsep_transport_controller_unittest.cc
+++ b/pc/jsep_transport_controller_unittest.cc
@@ -305,10 +305,14 @@
   // JsepTransportController::Observer overrides.
   bool OnTransportChanged(const std::string& mid,
                           RtpTransportInternal* rtp_transport,
-                          cricket::DtlsTransportInternal* dtls_transport,
+                          rtc::scoped_refptr<DtlsTransport> dtls_transport,
                           MediaTransportInterface* media_transport) override {
     changed_rtp_transport_by_mid_[mid] = rtp_transport;
-    changed_dtls_transport_by_mid_[mid] = dtls_transport;
+    if (dtls_transport) {
+      changed_dtls_transport_by_mid_[mid] = dtls_transport->internal();
+    } else {
+      changed_dtls_transport_by_mid_[mid] = nullptr;
+    }
     changed_media_transport_by_mid_[mid] = media_transport;
     return true;
   }