[MD Bookmarks] Remove the bookmarks-sidebar element.

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 46 matching lines @@
     });
 
     this.updateFromStore();
   },
 
   /** @return {HTMLElement} */
   getDropTarget: function() {
     return this.$.container;
   },
 
+  /** @return {boolean} */
+  isTopLevelFolder_: function() {
+    return this.depth == 0;
+  },
+
   /**
    * @private
    * @return {string}
    */
   getFolderIcon_: function() {
     return this.isSelectedFolder_ ? 'bookmarks:folder-open' : 'cr:folder';
   },
 
   /** @private */
   selectFolder_: function() {
@@ skipping 49 matching lines @@
    */
   isFolder_: function(itemId) {
     return !this.getState().nodes[itemId].url;
   },
 
   /**
    * @private
    * @return {boolean}
    */
   isRootFolder_: function() {
-    return this.depth == 0;
+    return this.itemId == ROOT_NODE_ID;
   },
 });