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

ui/aura/test/aura_test_helper.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/aura/test/aura_test_helper.h"
 
 #include "base/message_loop.h"
+#include "base/run_loop.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/env.h"
 #include "ui/aura/focus_manager.h"
 #include "ui/aura/monitor_manager.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/shared/root_window_capture_client.h"
 #include "ui/aura/single_monitor_manager.h"
 #include "ui/aura/test/test_activation_client.h"
 #include "ui/aura/test/test_screen.h"
 #include "ui/aura/test/test_stacking_client.h"
@@ skipping 53 matching lines @@
   stacking_client_.reset();
   test_activation_client_.reset();
   root_window_capture_client_.reset();
   focus_manager_.reset();
   root_window_.reset();
   aura::Env::DeleteInstance();
 }
 
 void AuraTestHelper::RunAllPendingInMessageLoop() {
 #if !defined(OS_MACOSX)
-  message_loop_->RunAllPendingWithDispatcher(
-      Env::GetInstance()->GetDispatcher());
+  // TODO(jbates) crbug.com/134753 Find quitters of this RunLoop and have them
+  //              use run_loop.QuitClosure().
+  base::RunLoop run_loop(Env::GetInstance()->GetDispatcher());
+  run_loop.RunUntilIdle();
 #endif
 }
 
 }  // namespace test
 }  // namespace aura