Add missing IWYU message_loop.h includes.

components/data_reduction_proxy/core/browser/data_reduction_proxy_settings_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 "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/md5.h"
+#include "base/message_loop/message_loop.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/test/histogram_tester.h"
 #include "base/test/mock_entropy_provider.h"
 #include "base/test/simple_test_clock.h"
 #include "base/time/clock.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_config.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_settings_test_utils.h"
@@ skipping 737 matching lines @@
   ASSERT_EQ(kNumDaysInHistory, result.size());
 
   for (size_t i = 0; i < kNumDaysInHistory; ++i) {
     long expected_length =
         static_cast<long>((kNumDaysInHistory - 1 - i) * 2);
     ASSERT_EQ(expected_length, result[i]);
   }
 }
 
 }  // namespace data_reduction_proxy