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

content/shell/browser/layout_test/layout_test_javascript_dialog_manager.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 CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_JAVASCRIPT_DIALOG_MANAGER_H_
 #define CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_JAVASCRIPT_DIALOG_MANAGER_H_
 
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
@@ skipping 11 matching lines @@
   void RunJavaScriptDialog(WebContents* web_contents,
                            const GURL& origin_url,
                            const std::string& accept_lang,
                            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(WebContents* web_contents,
-                             const base::string16& message_text,
                              bool is_reload,
                              const DialogClosedCallback& callback) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayoutTestJavaScriptDialogManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_BROWSER_LAYOUT_TEST_LAYOUT_TEST_JAVASCRIPT_DIALOG_MANAGER_H_