Add missing IWYU message_loop.h includes.

components/safe_browsing_db/v4_local_database_manager_unittest.cc

 // Copyright 2016 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/safe_browsing_db/v4_local_database_manager.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/test_simple_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/safe_browsing_db/v4_database.h"
 #include "components/safe_browsing_db/v4_test_util.h"
 #include "content/public/test/test_browser_thread_bundle.h"
 #include "crypto/sha2.h"
 #include "net/url_request/test_url_fetcher_factory.h"
 #include "testing/platform_test.h"
 
@@ skipping 934 matching lines @@
 
   TestClient client(SB_THREAT_TYPE_BINARY_MALWARE_URL, url_chain);
   EXPECT_FALSE(
       v4_local_database_manager_->CheckDownloadUrl(url_chain, &client));
   EXPECT_FALSE(client.on_check_download_urls_result_called_);
   WaitForTasksOnTaskRunner();
   EXPECT_TRUE(client.on_check_download_urls_result_called_);
 }
 
 }  // namespace safe_browsing