Add missing IWYU message_loop.h includes.

chromeos/network/host_resolver_impl_chromeos_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 "chromeos/network/host_resolver_impl_chromeos.h"
 
 #include <memory>
 
 #include "base/location.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/shill_device_client.h"
 #include "chromeos/dbus/shill_ipconfig_client.h"
 #include "chromeos/dbus/shill_service_client.h"
 #include "chromeos/network/device_state.h"
 #include "chromeos/network/network_state.h"
@@ skipping 135 matching lines @@
   info.set_address_family(net::ADDRESS_FAMILY_IPV6);
   EXPECT_EQ(net::OK, CallResolve(info));
   ASSERT_EQ(2u, addresses_.size());
   expected = base::StringPrintf("[%s]:%d", kTestIPv6Address, 0);
   EXPECT_EQ(expected, addresses_[0].ToString());
   expected = base::StringPrintf("%s:%d", kTestIPv4Address, 0);
   EXPECT_EQ(expected, addresses_[1].ToString());
 }
 
 }  // namespace chromeos