update elements and fix some bugs

test/iron_selector_activate_event_test.dart

Index: test/iron_selector_activate_event_test.dart
diff --git a/test/iron_selector_activate_event_test.dart b/test/iron_selector_activate_event_test.dart
index 05ecbeef128774bcf122ec56a8700a60045a5e10..c26355d3a187a7bf54667bdd09f3308b0136a322 100644
--- a/test/iron_selector_activate_event_test.dart
+++ b/test/iron_selector_activate_event_test.dart
@@ -112,5 +112,16 @@ main() async {
       // shouldn't got selected since we preventDefault in iron-activate
       expect(s.selected, '0');
     });
+    
+    test('activates after detach and re-attach', () {
+      // Detach and re-attach
+      var parent = s.parentNode;
+      s.remove();
+      parent.append(s);
+      
+      // select Item 2
+      s.children[2].dispatchEvent(new CustomEvent('tap', canBubble: true));
+      expect(s.selected, 2);
+    });
   });
 }