Add missing IWYU message_loop.h includes.

net/url_request/url_fetcher_impl_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/url_request/url_fetcher_impl.h"
 
 #include <stdint.h>
 #include <string.h>
 
 #include <algorithm>
 #include <limits>
 #include <memory>
 #include <string>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.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/task_scheduler/post_task.h"
 #include "base/test/scoped_task_environment.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/platform_thread.h"
@@ skipping 1540 matching lines @@
   EXPECT_EQ(-1, delegate.fetcher()->GetResponseCode());
   EXPECT_FALSE(delegate.fetcher()->GetResponseHeaders());
   std::string data;
   EXPECT_TRUE(delegate.fetcher()->GetResponseAsString(&data));
   EXPECT_TRUE(data.empty());
 }
 
 }  // namespace
 
 }  // namespace net