Add missing IWYU message_loop.h includes.

net/log/file_net_log_observer_unittest.cc

 // Copyright 2016 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/log/file_net_log_observer.h"
 
 #include <math.h>
 
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread.h"
 #include "base/values.h"
 #include "net/base/test_completion_callback.h"
 #include "net/log/net_log_entry.h"
 #include "net/log/net_log_event_type.h"
 #include "net/log/net_log_parameters_callback.h"
 #include "net/log/net_log_source.h"
 #include "net/log/net_log_source_type.h"
@@ skipping 756 matching lines @@
   // Check that there are events written to all files.
   for (int i = 0; i < kTotalNumFiles; i++) {
     ASSERT_GE(GetFileSize(GetEventFilePath(i)),
               static_cast<int64_t>(kEventSize));
   }
 }
 
 }  // namespace
 
 }  // namespace net