[MD Bookmarks] Add Select for Bookmarks.

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',
 
   properties: {
     /** @type {BookmarkTreeNode} */
     item: Object,
 
-    isSelected: {
+    isSelectedFolder: {
       type: Boolean,
       value: false,
       reflectToAttribute: true,
     },
   },
 
   /**
    * @private
    * @return {string}
    */
   getFolderIcon_: function() {
-    return this.isSelected ? 'bookmarks:folder-open' : 'cr:folder';
+    return this.isSelectedFolder ? 'bookmarks:folder-open' : 'cr:folder';
   },
 
   /**
    * @private
    * @return {string}
    */
   getArrowIcon_: function() {
     return this.item.isOpen ? 'cr:arrow-drop-up' : 'cr:arrow-drop-down';
   },
 
@@ skipping 17 matching lines @@
    * @private
    * @return {boolean}
    */
   hasChildFolder_: function() {
     for (var i = 0; i < this.item.children.length; i++) {
       if (!this.item.children[i].url)
         return true;
     }
     return false;
   },
+
+  /**
+   * @param {BookmarkTreeNode} item
+   * @private
+   * @return {boolean}
+   */
+  isFolder_: function(item) {
+    return !item.url;
+  }
 });