Adding placeholder ortc_unittests target.

webrtc/ortc/dummy_test.cc

+/*
+ *  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/test/gtest.h"
+
+// This is just a placeholder test so that trybots can be updated to run the
+// new "ortc_unittests" target.
+TEST(DummyOrtcTest, Test) {
+}