Add missing IWYU message_loop.h includes.

components/autofill/core/browser/webdata/web_data_service_unittest.cc

 // Copyright 2013 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 <memory>
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/location.h"
 #include "base/macros.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/single_thread_task_runner.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/test/scoped_task_environment.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
@@ skipping 515 matching lines @@
   // Check that the credit card was removed.
   AutofillWebDataServiceConsumer<std::vector<std::unique_ptr<CreditCard>>>
       card_consumer2;
   handle2 = wds_->GetCreditCards(&card_consumer2);
   base::RunLoop().Run();
   EXPECT_EQ(handle2, card_consumer2.handle());
   ASSERT_EQ(0U, card_consumer2.result().size());
 }
 
 }  // namespace autofill