Add missing IWYU message_loop.h includes.

chrome/browser/apps/app_shim/app_shim_host_manager_browsertest_mac.mm

 // Copyright 2013 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 "chrome/browser/apps/app_shim/app_shim_host_manager_mac.h"
 
 #include <unistd.h>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/threading/thread_restrictions.h"
 #include "chrome/browser/apps/app_shim/app_shim_handler_mac.h"
 #include "chrome/browser/apps/app_shim/test/app_shim_host_manager_test_api_mac.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/mac/app_mode_common.h"
 #include "chrome/common/mac/app_shim_messages.h"
@@ skipping 268 matching lines @@
   ASSERT_TRUE(base::ReadSymbolicLink(symlink_path_, &socket_path));
   EXPECT_EQ(app_mode::kAppShimSocketShortName, socket_path.BaseName().value());
 
   // Check that the RunningChromeVersion file is correctly written.
   base::FilePath version;
   EXPECT_TRUE(base::ReadSymbolicLink(version_path_, &version));
   EXPECT_EQ(version_info::GetVersionNumber(), version.value());
 }
 
 }  // namespace