Add missing IWYU message_loop.h includes.

chrome/browser/local_discovery/service_discovery_client_unittest.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 <stdint.h>
 
 #include "base/location.h"
 #include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/local_discovery/service_discovery_client_impl.h"
 #include "net/base/net_errors.h"
 #include "net/dns/dns_protocol.h"
 #include "net/dns/mdns_client_impl.h"
 #include "net/dns/mock_mdns_socket_factory.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 487 matching lines @@
                          ServiceResolver::STATUS_REQUEST_TIMEOUT, _, _, _));
 
   // TODO(noamsml): When NSEC record support is added, change this to use an
   // NSEC record.
   RunFor(base::TimeDelta::FromSeconds(4));
 }
 
 }  // namespace
 
 }  // namespace local_discovery