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

base/test/test_support_android.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 <stdarg.h>
 #include <string.h>
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/memory/singleton.h"
+#include "base/message_loop.h"
 #include "base/message_pump_android.h"
 #include "base/path_service.h"
 #include "base/synchronization/waitable_event.h"
 
 namespace {
 
 // The test implementation of AndroidOS stores everything in the following
 // directory.
 const char* kAndroidTestTempDirectory = "/data/local/tmp";
 
@@ skipping 173 matching lines @@
 void InitAndroidTestMessageLoop() {
   MessageLoop::InitMessagePumpForUIFactory(&CreateMessagePumpForUIStub);
 }
 
 void InitAndroidTest() {
   InitAndroidTestLogging();
   InitAndroidTestPaths();
   InitAndroidTestMessageLoop();
 }
 }  // namespace base