Run queued tasks before shutting down after running a layout test.

content/shell/browser/layout_test/layout_test_browser_main.cc

 // Copyright 2014 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 "content/shell/browser/layout_test/layout_test_browser_main.h"
 
 #include <iostream>
 #include <memory>
 
 #include "base/command_line.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/logging.h"
+#include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "content/public/browser/browser_main_runner.h"
 #include "content/public/common/url_constants.h"
 #include "content/shell/browser/layout_test/blink_test_controller.h"
 #include "content/shell/browser/layout_test/test_info_extractor.h"
@@ skipping 109 matching lines @@
           switches::kCheckLayoutTestSysDeps)) {
     base::ThreadTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::MessageLoop::QuitWhenIdleClosure());
     main_runner->Run();
     content::Shell::CloseAllWindows();
     main_runner->Shutdown();
     return 0;
   }
 
   exit_code = RunTests(main_runner);
+  base::RunLoop().RunUntilIdle();
 
 #if !defined(OS_ANDROID)
   main_runner->Shutdown();
 #endif
 
   return exit_code;
 }