Add the beginning of a simple window manager that we'll support on Windows.

mash/simple_wm/main.cc

+// Copyright 2016 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 "mash/simple_wm/simple_wm.h"
+#include "services/service_manager/public/c/main.h"
+#include "services/service_manager/public/cpp/service_runner.h"
+
+MojoResult ServiceMain(MojoHandle service_request_handle) {
+  service_manager::ServiceRunner runner(new simple_wm::SimpleWM);
+  return runner.Run(service_request_handle);
+}