It turns out the Cleanup() method in JsModalDialog is not

chrome/browser/ui/app_modal_dialogs/js_modal_dialog.h

 // Copyright (c) 2010 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_UI_APP_MODAL_DIALOGS_JS_MODAL_DIALOG_H_
 #define CHROME_BROWSER_UI_APP_MODAL_DIALOGS_JS_MODAL_DIALOG_H_
 #pragma once
 
 #include <string>
 
@@ skipping 60 matching lines @@
   void OnAccept(const std::wstring& prompt_text, bool suppress_js_messages);
   void OnClose();
 
   // Accessors
   int dialog_flags() const { return dialog_flags_; }
   std::wstring message_text() const { return message_text_; }
   std::wstring default_prompt_text() const { return default_prompt_text_; }
   bool display_suppress_checkbox() const { return display_suppress_checkbox_; }
   bool is_before_unload_dialog() const { return is_before_unload_dialog_; }
 
- protected:
-  // Overridden from AppModalDialog:
-  virtual void Cleanup();
-
  private:
   // Overridden from NotificationObserver:
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details);
 
   // Initializes for notifications to listen.
   void InitNotifications();
 
   NotificationRegistrar registrar_;
@@ skipping 13 matching lines @@
   std::wstring message_text_;
   std::wstring default_prompt_text_;
   bool display_suppress_checkbox_;
   bool is_before_unload_dialog_;
   IPC::Message* reply_msg_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptAppModalDialog);
 };
 
 #endif  // CHROME_BROWSER_UI_APP_MODAL_DIALOGS_JS_MODAL_DIALOG_H_