Remove the ability of webpages to specify strings for the onbeforeunload dialog.

extensions/browser/guest_view/web_view/javascript_dialog_helper.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_GUEST_VIEW_WEB_VIEW_JAVASCRIPT_DIALOG_HELPER_H_
 #define EXTENSIONS_BROWSER_GUEST_VIEW_WEB_VIEW_JAVASCRIPT_DIALOG_HELPER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/javascript_dialog_manager.h"
 
@@ skipping 10 matching lines @@
   void RunJavaScriptDialog(
       content::WebContents* web_contents,
       const GURL& origin_url,
       const std::string& accept_lang,
       content::JavaScriptMessageType javascript_message_type,
       const base::string16& message_text,
       const base::string16& default_prompt_text,
       const DialogClosedCallback& callback,
       bool* did_suppress_message) override;
   void RunBeforeUnloadDialog(content::WebContents* web_contents,
-                             const base::string16& message_text,
                              bool is_reload,
                              const DialogClosedCallback& callback) override;
   bool HandleJavaScriptDialog(content::WebContents* web_contents,
                               bool accept,
                               const base::string16* prompt_override) override;
   void CancelActiveAndPendingDialogs(
       content::WebContents* web_contents) override;
   void ResetDialogState(content::WebContents* web_contents) override;
 
  private:
   void OnPermissionResponse(
       const DialogClosedCallback& callback,
       bool allow,
       const std::string& user_input);
 
   // Pointer to the webview that is being helped.
   WebViewGuest* const web_view_guest_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptDialogHelper);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_GUEST_VIEW_WEB_VIEW_JAVASCRIPT_DIALOG_HELPER_H_