Add missing IWYU message_loop.h includes.

chrome/browser/policy/cloud/cloud_policy_invalidator_unittest.cc

 // Copyright 2013 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/policy/cloud/cloud_policy_invalidator.h"
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/sample_map.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/run_loop.h"
 #include "base/test/simple_test_clock.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "build/build_config.h"
@@ skipping 1070 matching lines @@
     CloudPolicyInvalidatorUserTypedTest,
     testing::Values(em::DeviceRegisterRequest::ANDROID_BROWSER));
 #else
 INSTANTIATE_TEST_CASE_P(
     CloudPolicyInvalidatorUserTypedTestInstance,
     CloudPolicyInvalidatorUserTypedTest,
     testing::Values(em::DeviceRegisterRequest::BROWSER));
 #endif
 
 }  // namespace policy