Move RtpTransportControllerSend to a new file.

webrtc/call/rtp_transport_controller_send.cc

+/*
+ *  Copyright (c) 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/call/rtp_transport_controller_send.h"
+
+namespace webrtc {
+
+RtpTransportControllerSend::RtpTransportControllerSend(
+    Clock* clock,
+    webrtc::RtcEventLog* event_log)
+    : send_side_cc_(clock, nullptr /* observer */, event_log, &packet_router_) {
+}
+
+void RtpTransportControllerSend::RegisterNetworkObserver(
+    SendSideCongestionController::Observer* observer) {
+  // Must be called only once.

[the sun, 2017/04/18 10:05:35]

DCHECK that instead, possibly in the SendSideCC (not clear to me whether the
constraint is on RtpTransportControllerSend or SendSideCongestionController).

[nisse-webrtc, 2017/04/18 11:48:30]

There already is a DCHECK in the SendSideCC method. Do you want me to delete
this comment?

+  send_side_cc_.RegisterNetworkObserver(observer);
+}
+
+}  // namespace webrtc