Add an XPC implementation of sandbox::MessageServer.

sandbox/mac/xpc.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 "sandbox/mac/xpc.h"
+
+namespace sandbox {
+
+bool InitializeXPC() {
+  std::vector<std::string> path_list;
+  path_list.push_back("/usr/lib/system/libxpc.dylib");
+
+  sandbox_mac::StubPathMap path_map;
+  path_map[sandbox_mac::kModuleXpc_stubs] = path_list;
+  path_map[sandbox_mac::kModuleXpc_private_stubs] = path_list;
+
+  return sandbox_mac::InitializeStubs(path_map);
+}
+
+}  // namespace sandbox