Add missing IWYU message_loop.h includes.

chrome/browser/sync/test/integration/passwords_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/passwords_helper.h"
 
 #include <sstream>
 #include <utility>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/time/time.h"
 #include "chrome/browser/password_manager/password_store_factory.h"
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 #include "chrome/browser/sync/test/integration/profile_sync_service_harness.h"
 #include "chrome/browser/sync/test/integration/sync_datatype_helper.h"
 #include "components/password_manager/core/browser/password_manager_test_utils.h"
 #include "components/password_manager/core/browser/password_store.h"
@@ skipping 259 matching lines @@
     result =
         passwords_helper::ProfileContainsSamePasswordFormsAsVerifier(index_);
   } while (needs_recheck_);
   in_progress_ = false;
   return result;
 }
 
 std::string SamePasswordFormsAsVerifierChecker::GetDebugMessage() const {
   return "Waiting for passwords to match verifier";
 }