Add a minimal RtpTransport class for use by BaseChannel.

webrtc/pc/rtptransport.cc

Index: webrtc/pc/rtptransport.cc
diff --git a/webrtc/pc/rtptransport.cc b/webrtc/pc/rtptransport.cc
new file mode 100644
index 0000000000000000000000000000000000000000..eb463db0bfb53afd7a045ca38613aac7479b10ae
--- /dev/null
+++ b/webrtc/pc/rtptransport.cc
@@ -0,0 +1,23 @@
+/*
+ *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/pc/rtptransport.h"
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+void RtpTransport::set_rtcp_packet_transport(
+    rtc::PacketTransportInternal* rtcp) {
+  RTC_DCHECK(!rtcp_mux_required_);
+  rtcp_packet_transport_ = rtcp;
+}
+
+}  // namespace webrtc