Add missing IWYU message_loop.h includes.

chrome/browser/sync/test/integration/bookmarks_helper.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 "chrome/browser/sync/test/integration/bookmarks_helper.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <set>
 #include <stack>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/rand_util.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/threading/thread_restrictions.h"
@@ skipping 927 matching lines @@
 }  // namespace
 
 BookmarksUrlChecker::BookmarksUrlChecker(int profile,
                                          const GURL& url,
                                          int expected_count)
     : AwaitMatchStatusChangeChecker(base::Bind(BookmarkCountsByUrlMatch,
                                                profile,
                                                base::ConstRef(url),
                                                expected_count),
                                     "Bookmark URL counts match.") {}