Add missing IWYU message_loop.h includes.

net/proxy/proxy_config_service_linux_unittest.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 "net/proxy/proxy_config_service_linux.h"
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/format_macros.h"
 #include "base/location.h"
 #include "base/logging.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "net/proxy/proxy_config.h"
 #include "net/proxy/proxy_config_service_common_unittest.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 1644 matching lines @@
     EXPECT_EQ(ProxyConfigService::CONFIG_VALID,
               sync_config_getter.SyncGetLatestProxyConfig(&config));
     EXPECT_FALSE(config.auto_detect());
     EXPECT_TRUE(slaverc5_rules.Matches(config.proxy_rules()));
   }
 }
 
 }  // namespace
 
 }  // namespace net