Add missing IWYU message_loop.h includes.

components/data_reduction_proxy/core/browser/data_reduction_proxy_config_service_client_unittest.cc

 // Copyright 2015 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 "components/data_reduction_proxy/core/browser/data_reduction_proxy_config_service_client.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/base64.h"
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/metrics/field_trial.h"
 #include "base/run_loop.h"
 #include "base/test/histogram_tester.h"
 #include "base/test/mock_entropy_provider.h"
 #include "base/time/time.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_config_test_utils.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_configurator.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_mutable_config_values.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_test_utils.h"
@@ skipping 1275 matching lines @@
     histogram_tester.ExpectTotalCount(
         "DataReductionProxy.ConfigService.FetchLatency", 1);
     EXPECT_EQ(base::TimeDelta::FromSeconds(kConfigRefreshDurationSeconds),
               config_client()->GetDelay());
     VerifyRemoteSuccess(true);
   }
 }
 #endif
 
 }  // namespace data_reduction_proxy