dcsctp: Adding testing macros

This is the first and last macro that will go into this project,
but it's really useful to verify that a call returns an optional
value (that is non-nullopt) and that extracts the underlying type.

Bug: webrtc:12614
Change-Id: I0a05bf22466a575dbcc9a8f7b88dde0f55ff54d9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213345
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33607}

net/dcsctp/testing/BUILD.gn

@@ -0,0 +1,14 @@
+# Copyright (c) 2021 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.
+
+import("../../../webrtc.gni")
+
+rtc_source_set("testing_macros") {
+  testonly = true
+  sources = [ "testing_macros.h" ]
+}