fixes to polymer, gets tests back to a stable state

samples/third_party/todomvc/web/editable_label.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library todomvc.web.editable_label;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 
 /**
  * Label whose [value] can be edited by double clicking. When editing, it
  * displays a form and input element, otherwise it displays the label.
  */
 // For illustration purposes this type uses Polymer.register instead of
 // CustomTag. We must mark it @reflectable to ensure its members
 // (the event handlers) are preserved and can be referenced from HTML.
 @reflectable
 class EditableLabel extends PolymerElement {
   @observable bool editing = false;
   @published String value = '';
 
   factory EditableLabel() => new Element.tag('editable-label');
 
   EditableLabel.created() : super.created();
 
   bool get applyAuthorStyles => true;
 
-  InputElement get _editBox => getShadowRoot("editable-label").query('#edit');
+  ShadowRoot get _shadowRoot => getShadowRoot('editable-label');
+
+  InputElement get _editBox => _shadowRoot.query('#edit');
 
   void edit() {
     editing = true;
 
-    // This causes _editBox to be inserted.
-    performMicrotaskCheckpoint();
-
-    // For IE and Firefox: use .focus(), then reset the value to move the
-    // cursor to the end.
-    _editBox.focus();
-    _editBox.value = '';
-    _editBox.value = value;
+    // Wait for _editBox to be inserted.
+    onMutation(_shadowRoot, (_) {
+      // For IE and Firefox: use .focus(), then reset the value to move the
+      // cursor to the end.
+      _editBox.focus();
+      _editBox.value = '';
+      _editBox.value = value;
+    });
   }
 
   void update(Event e) {
     e.preventDefault(); // don't submit the form
     if (!editing) return; // bail if user canceled
     value = _editBox.value;
     editing = false;
   }
 
   void maybeCancel(KeyboardEvent e) {
     if (e.keyCode == KeyCode.ESC) {
       editing = false;
     }
   }
 }
 
 @initMethod
 void _init() {
   Polymer.register('editable-label', EditableLabel);
 }