Get mojo_shell building inside chromium checkout.

mojo/shell/application_manager/test.mojom

+// Copyright 2014 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.
+
+module mojo.shell;
+
+interface TestService {
+  Test(string test_string) => ();
+};
+
+interface TestA {
+  CallB();
+  CallCFromB();
+};
+
+interface TestB {
+  B() => ();
+  CallC() => ();
+};
+
+interface TestC {
+  C() => ();
+};