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

mojo/services/test_service/test_service_impl.cc

 // 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.
 
-#include "mojo/shell/shell_test_base.h"
+#include "mojo/services/test_service/test_service_impl.h"
 
 namespace mojo {
-namespace shell {
 namespace test {
 
-ShellTestBase::ShellTestBase() {
+TestServiceImpl::TestServiceImpl() {
 }
 
-ShellTestBase::~ShellTestBase() {
+TestServiceImpl::~TestServiceImpl() {
+}
+
+void TestServiceImpl::Ping(const mojo::Callback<void()>& callback) {
+  callback.Run();
 }
 
 }  // namespace test
-}  // namespace shell
 }  // namespace mojo