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

chrome/browser/tab_contents/render_view_context_menu_browsertest_util.h

 // 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.
 
 #ifndef CHROME_BROWSER_TAB_CONTENTS_RENDER_VIEW_CONTEXT_MENU_BROWSERTEST_UTIL_H_
 #define CHROME_BROWSER_TAB_CONTENTS_RENDER_VIEW_CONTEXT_MENU_BROWSERTEST_UTIL_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 class RenderViewContextMenu;
 
 class ContextMenuNotificationObserver : public content::NotificationObserver {
  public:
   // Wait for a context menu to be shown, and then execute |command_to_execute|.
-  // As the context menu might spin a nested message loop, the usual way to wait
-  // for the result of the |command_to_execute|, i.e. running
-  // ui_test_utils::WindowedNotificationObserver::Wait, won't work. The
-  // ContextMenuNotificationObserver can work around this problem. In order to
-  // do so, you need to also specify what notification the
-  // WindowedNotificationObserver is waiting for.
-  ContextMenuNotificationObserver(int command_to_execute,
-                                  int expected_notification);
+  explicit ContextMenuNotificationObserver(int command_to_execute);
   virtual ~ContextMenuNotificationObserver();
 
  private:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   void ExecuteCommand(RenderViewContextMenu* context_menu);
 
   content::NotificationRegistrar registrar_;
   int command_to_execute_;
-  int expected_notification_;
-  bool seen_expected_notification_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextMenuNotificationObserver);
 };
 
 #endif  // CHROME_BROWSER_TAB_CONTENTS_RENDER_VIEW_CONTEXT_MENU_BROWSERTEST_UTIL_H_