Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

ui/views/examples/content_client/examples_browser_main_parts.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 "ui/views/examples/content_client/examples_browser_main_parts.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/message_loop.h"
+#include "base/run_loop.h"
 #include "base/string_number_conversions.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "content/public/common/content_switches.h"
 #include "content/shell/shell_browser_context.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/net_module.h"
 #include "ui/views/examples/examples_window.h"
 #include "ui/views/focus/accelerator_handler.h"
 #include "ui/views/test/test_views_delegate.h"
@@ skipping 50 matching lines @@
 #if defined(USE_AURA)
   stacking_client_.reset();
   aura::Env::DeleteInstance();
 #endif
 }
 
 bool ExamplesBrowserMainParts::MainMessageLoopRun(int* result_code) {
   // xxx: Hax here because this kills event handling.
 #if !defined(USE_AURA)
   views::AcceleratorHandler accelerator_handler;
-  MessageLoopForUI::current()->RunWithDispatcher(&accelerator_handler);
+  base::RunLoop run_loop(&accelerator_handler);
 #else
-  MessageLoopForUI::current()->Run();
+  base::RunLoop run_loop;
 #endif
+  run_loop.Run();
   return true;
 }
 
 }  // namespace examples
 }  // namespace views