DOMUI Prefs: Add a deletable item list type, and use it for startup pages.

chrome/browser/resources/options/browser_options_startup_page_list.js

 // Copyright (c) 2010 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.browser_options', function() {
-  const List = cr.ui.List;
+  const DeletableItemList = options.DeletableItemList;
   const ListItem = cr.ui.ListItem;
 
   /**
    * Creates a new startup page list item.
    * @param {Object} pageInfo The page this item represents.
    * @constructor
    * @extends {cr.ui.ListItem}
    */
   function StartupPageListItem(pageInfo) {
     var el = cr.doc.createElement('div');
@@ skipping 26 matching lines @@
                                           this.pageInfo_['url']);
       titleEl.title = this.pageInfo_['tooltip'];
 
       this.appendChild(titleEl);
     },
   };
 
   var StartupPageList = cr.ui.define('list');
 
   StartupPageList.prototype = {
-    __proto__: List.prototype,
+    __proto__: DeletableItemList.prototype,
 
     /** @inheritDoc */
-    createItem: function(pageInfo) {
+    createItemContents: function(pageInfo) {
       return new StartupPageListItem(pageInfo);
     },
+
+    /** @inheritDoc */
+    deleteItemAtIndex: function(index) {
+      chrome.send('removeStartupPages', [String(index)]);
+    },
   };
 
   return {
     StartupPageList: StartupPageList
   };
 });