Add a warning when developing an extension that uses old manifest version.

chrome/browser/resources/extensions/extension_list.js

 // Copyright (c) 2012 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.
 
 cr.define('options', function() {
   'use strict';
 
   /**
    * A lookup helper function to find the first node that has an id (starting
    * at |node| and going up the parent chain).
@@ skipping 242 matching lines @@
           list.appendChild(document.createElement('li')).innerText = warning;
         });
       }
 
       // The install warnings.
       if (extension.installWarnings) {
         var panel = node.querySelector('.install-warnings');
         panel.hidden = false;
         var list = panel.querySelector('ul');
         extension.installWarnings.forEach(function(warning) {
-          list.appendChild(document.createElement('li')).innerText = warning;
+          var li = document.createElement('li');
+          li[warning.isHTML ? 'innerHTML' : 'innerText'] = warning.message;
+          list.appendChild(li);
         });
       }
 
       this.appendChild(node);
     }
   };
 
   return {
     ExtensionsList: ExtensionsList
   };
 });