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

content/shell/browser/layout_test/layout_test_javascript_dialog_manager.cc

 // 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.
 
 #include "content/shell/browser/layout_test/layout_test_javascript_dialog_manager.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 17 matching lines @@
     const base::string16& message_text,
     const base::string16& default_prompt_text,
     const DialogClosedCallback& callback,
     bool* did_suppress_message) {
   callback.Run(true, base::string16());
   return;
 }
 
 void LayoutTestJavaScriptDialogManager::RunBeforeUnloadDialog(
     WebContents* web_contents,
-    const base::string16& message_text,
     bool is_reload,
     const DialogClosedCallback& callback) {
   callback.Run(true, base::string16());
   return;
 }
 
 }  // namespace content