Add missing IWYU message_loop.h includes.

chrome/browser/browsing_data/browsing_data_database_helper_browsertest.cc

 // Copyright (c) 2012 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 <stdint.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/files/file_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/browsing_data/browsing_data_database_helper.h"
 #include "chrome/browser/browsing_data/browsing_data_helper_browsertest.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/test/test_browser_thread.h"
 #include "content/public/test/test_utils.h"
 
@@ skipping 125 matching lines @@
                  base::Unretained(&callback)));
 
   std::list<BrowsingDataDatabaseHelper::DatabaseInfo> result =
       callback.result();
 
   ASSERT_EQ(1u, result.size());
   EXPECT_EQ(origin_str, result.begin()->identifier.ToString());
   EXPECT_STREQ(db, result.begin()->database_name.c_str());
 }
 }  // namespace