[WIP] Add DCHECK for mojo::edk::Init().

chromecast/app/cast_unittests_main.cc

+// 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.
+
+#include "base/test/test_io_thread.h"
+#include "chromecast/app/cast_test_launcher.h"
+#include "mojo/edk/embedder/embedder.h"
+#include "mojo/edk/test/scoped_ipc_support.h"
+
+int main(int argc, char* argv[]) {
+  mojo::edk::Init();
+  base::TestIOThread test_io_thread(base::TestIOThread::kAutoStart);
+  mojo::edk::test::ScopedIPCSupport ipc_support(test_io_thread.task_runner());
+  return chromecast::shell::LaunchTests(argc, argv);
+}