Add missing IWYU message_loop.h includes.

chrome/browser/devtools/devtools_sanity_browsertest.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 <stddef.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/cancelable_callback.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.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/path_service.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task_scheduler/post_task.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
@@ skipping 2043 matching lines @@
   RunTestFunction(window, "testWindowInitializedOnNavigateBack");
 
   DevToolsWindowTesting::CloseDevToolsWindowSync(window);
   content::WebUIControllerFactory::UnregisterFactoryForTesting(&test_factory);
 }
 
 // Tests scripts panel showing.
 IN_PROC_BROWSER_TEST_F(DevToolsSanityTest, TestDevToolsSharedWorker) {
   RunTest("testDevToolsSharedWorker", url::kAboutBlankURL);
 }