Add missing IWYU message_loop.h includes.

chrome/browser/chromeos/net/network_state_notifier_unittest.cc

 // 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 "chrome/browser/chromeos/net/network_state_notifier.h"
 
 #include <memory>
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/shill_device_client.h"
 #include "chromeos/dbus/shill_service_client.h"
 #include "chromeos/login/login_state.h"
 #include "chromeos/network/network_connect.h"
 #include "chromeos/network/network_handler.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 #include "third_party/cros_system_api/dbus/service_constants.h"
@@ skipping 103 matching lines @@
   base::RunLoop().RunUntilIdle();
   // Failure should spawn a notification.
   message_center::MessageCenter* message_center =
       message_center::MessageCenter::Get();
   EXPECT_TRUE(message_center->FindVisibleNotificationById(
       NetworkStateNotifier::kNetworkConnectNotificationId));
 }
 
 }  // namespace test
 }  // namespace chromeos