[MD Bookmarks] Add lines between items and no search results message.

chrome/browser/resources/md_bookmarks/store.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.
 
 var BookmarksStore = Polymer({
   is: 'bookmarks-store',
 
   properties: {
     /** @type {BookmarkTreeNode} */
     rootNode: {
       type: Object,
       notify: true,
     },
 
     /** @type {?string} */
     selectedId: {
       type: String,
       observer: 'updateSelectedDisplay_',
       notify: true,
     },
 
     searchTerm: {
       type: String,
+      value: '',
       observer: 'updateSearchDisplay_',
       notify: true,
     },
 
     /**
      * This updates to either the result of a search or the contents of the
      * selected folder.
      * @type {Array<BookmarkTreeNode>}
      */
     displayedList: {
@@ skipping 74 matching lines @@
   isAncestorOfSelected_: function(folder) {
     if (!this.selectedId)
       return false;
 
     var selectedNode = this.idToNodeMap_[this.selectedId];
     return selectedNode.path.startsWith(folder.path);
   },
 
   /** @private */
   updateSearchDisplay_: function() {
+    if (!this.rootNode)
+      return;
+
     if (!this.searchTerm) {
       this.fire('selected-folder-changed', this.rootNode.children[0].id);
     } else {
       chrome.bookmarks.search(this.searchTerm, function(results) {
         if (this.selectedId)
           this.deselectFolders_();
 
         this._setDisplayedList(results);
       }.bind(this));
     }
@@ skipping 147 matching lines @@
     idToNodeMap[bookmarkNode.id] = bookmarkNode;
 
   if (bookmarkNode.url)
     return;
 
   bookmarkNode.isSelected = false;
   bookmarkNode.isOpen = true;
   for (var i = 0; i < bookmarkNode.children.length; i++)
     BookmarksStore.initNodes(bookmarkNode.children[i], idToNodeMap);
 };