dbus: add ObjectPath type

dbus/mock_exported_object.cc

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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 "dbus/mock_exported_object.h"
 
 namespace dbus {
 
 MockExportedObject::MockExportedObject(Bus* bus,
                                        const std::string& service_name,
-                                       const std::string& object_path)
+                                       const ObjectPath& object_path)
     : ExportedObject(bus, service_name, object_path) {
 }
 
 MockExportedObject::~MockExportedObject() {
 }
 
 }  // namespace dbus