MD Bookmarks: Support policies for disabling bookmark editing

chrome/browser/resources/md_bookmarks/folder_node.js

 // Copyright 2016 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.
 
 Polymer({
   is: 'bookmarks-folder-node',
 
   behaviors: [
     bookmarks.StoreClient,
   ],
@@ skipping 61 matching lines @@
   /** @return {HTMLElement} */
   getFocusTarget: function() {
     return this.$.container;
   },
 
   /** @return {HTMLElement} */
   getDropTarget: function() {
     return this.$.container;
   },
 
-  /** @return {boolean} */
-  isTopLevelFolder_: function() {
-    return this.depth == 0;
-  },
-
   /**
    * @private
    * @param {!Event} e
    */
   onKeydown_: function(e) {
     var yDirection = 0;
     var xDirection = 0;
     var handled = true;
     if (e.key == 'ArrowUp') {
       yDirection = -1;
@@ skipping 243 matching lines @@
   },
 
   /**
    * @private
    * @return {string}
    */
   getTabIndex_: function() {
     return this.isSelectedFolder_ ? '0' : '';
   },
 });