Add missing IWYU message_loop.h includes.

chrome/browser/safe_browsing/incident_reporting/platform_state_store_win_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 "chrome/browser/safe_browsing/incident_reporting/platform_state_store.h"
 
 #include <utility>
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/test_reg_util_win.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/win/registry.h"
 #include "chrome/browser/prefs/browser_prefs.h"
 #include "chrome/test/base/testing_browser_process.h"
 #include "chrome/test/base/testing_profile.h"
 #include "chrome/test/base/testing_profile_manager.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_notifier_impl.h"
@@ skipping 156 matching lines @@
 
   std::string data;
   PlatformStateStoreLoadResult result = ReadStoreData(profile_, &data);
   EXPECT_EQ(PlatformStateStoreLoadResult::CLEARED_DATA, result);
   EXPECT_EQ(std::string(), data);
   AssertTestDataIsAbsent();
 }
 
 }  // namespace platform_state_store
 }  // namespace safe_browsing