RTCRtpSender with track behind RuntimeEnabled flag

third_party/WebKit/Source/modules/peerconnection/RTCRtpSender.idl

Index: third_party/WebKit/Source/modules/peerconnection/RTCRtpSender.idl
diff --git a/third_party/WebKit/Source/modules/peerconnection/RTCRtpSender.idl b/third_party/WebKit/Source/modules/peerconnection/RTCRtpSender.idl
new file mode 100644
index 0000000000000000000000000000000000000000..9b653b9a823d86dea3c23fb6f20759f903461610
--- /dev/null
+++ b/third_party/WebKit/Source/modules/peerconnection/RTCRtpSender.idl
@@ -0,0 +1,11 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://w3c.github.io/webrtc-pc/#rtcrtpsender-interface
+[
+    RuntimeEnabled=RTCRtpSender,
+] interface RTCRtpSender {
+    readonly attribute MediaStreamTrack? track;
+    // TODO(hbos): Implement the rest of RTCRtpSender, https://crbug.com/700916.
+};