Add missing IWYU message_loop.h includes.

net/tools/quic/synchronous_host_resolver.cc

 // Copyright (c) 2015 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 "net/tools/quic/synchronous_host_resolver.h"
 
 #include "base/at_exit.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/net_errors.h"
 #include "net/dns/host_resolver_impl.h"
 #include "net/log/net_log.h"
 #include "net/log/net_log_with_source.h"
 
@@ skipping 75 matching lines @@
 }  // namespace
 
 // static
 int SynchronousHostResolver::Resolve(const std::string& host,
                                      AddressList* addresses) {
   ResolverThread resolver;
   return resolver.Resolve(host, addresses);
 }
 
 }  // namespace net