Prevent popunders with the new auto-dismissing dialogs.

chrome/browser/ui/javascript_dialogs/javascript_dialog.h

 // Copyright 2016 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_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_
 #define CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_
 
+#include <memory>
+
 #include "base/memory/weak_ptr.h"
 #include "content/public/browser/javascript_dialog_manager.h"
 
+class AppModalDialogHelper;
+
 class JavaScriptDialog {
  public:
   virtual ~JavaScriptDialog();
 
   static base::WeakPtr<JavaScriptDialog> Create(
       content::WebContents* parent_web_contents,
       content::WebContents* alerting_web_contents,
       const base::string16& title,
       content::JavaScriptMessageType message_type,
       const base::string16& message_text,
       const base::string16& default_prompt_text,
       const content::JavaScriptDialogManager::DialogClosedCallback&
           dialog_callback);
 
   // Closes the dialog without sending a callback. This is useful when the
   // JavaScriptDialogTabHelper needs to make this dialog go away so that it can
   // respond to a call that requires it to make no callback or make a customized
   // one.
   virtual void CloseDialogWithoutCallback() = 0;
+
+ protected:
+  explicit JavaScriptDialog(content::WebContents* parent_web_contents);
+
+ private:
+  std::unique_ptr<AppModalDialogHelper> dialog_helper_;
 };
 
 #endif  // CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_H_