Mojo: Add a trivial end-to-end (in-process) test of Mojo shell.

mojo/services/test_service/test_service.mojom

Index: mojo/services/test_service/test_service.mojom
diff --git a/mojo/services/dbus_echo/echo.mojom b/mojo/services/test_service/test_service.mojom
similarity index 67%
copy from mojo/services/dbus_echo/echo.mojom
copy to mojo/services/test_service/test_service.mojom
index 937737c223cf423c989c0eb76b41b12bb0f6df0b..1065b20ab30847eca7a74f2ed21f5e31691f6ed4 100644
--- a/mojo/services/dbus_echo/echo.mojom
+++ b/mojo/services/test_service/test_service.mojom
@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module mojo {
+module mojo.test {
 
-interface EchoService {
-  Echo(string to_echo) => (string echoed);
+interface ITestService {
+  Ping() => ();
 };
 
-}
+}  // module mojo.test