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

chrome/browser/resources/md_bookmarks/store.js

Index: chrome/browser/resources/md_bookmarks/store.js
diff --git a/chrome/browser/resources/md_bookmarks/store.js b/chrome/browser/resources/md_bookmarks/store.js
index baddea20b2e1979feb20095a57cae3ba320e3edd..5a4b53b44b38174f3cfe0657f1a40fdb97003ce0 100644
--- a/chrome/browser/resources/md_bookmarks/store.js
+++ b/chrome/browser/resources/md_bookmarks/store.js
@@ -21,6 +21,7 @@ var BookmarksStore = Polymer({
 
     searchTerm: {
       type: String,
+      value: '',
       observer: 'updateSearchDisplay_',
       notify: true,
     },
@@ -110,6 +111,9 @@ var BookmarksStore = Polymer({
 
   /** @private */
   updateSearchDisplay_: function() {
+    if (!this.rootNode)
+      return;
+
     if (this.searchTerm == '') {
       this.fire('selected-folder-changed', this.rootNode.children[0].id);
     } else {