update elements and fix some bugs

test/paper_checkbox_test.dart

 // Copyright (c) 2015, 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.
 @TestOn('browser')
 library polymer_elements.test.paper_checkbox_test;
 
 import 'dart:async';
 import 'package:polymer_elements/paper_checkbox.dart';
 import 'package:polymer_interop/polymer_interop.dart';
 import 'package:web_components/web_components.dart';
@@ skipping 57 matching lines @@
     });
 
     test('disabled checkbox is always valid', () {
       c1.disabled = true;
       c1.required = true;
       expect(c1.validate(null), isTrue);
 
       c1.checked = true;
       expect(c1.validate(null), isTrue);
     });
-
-    test('checkbox label can be updated', () {
-      Polymer.dom(c1).text = 'Batman';
-      c1.updateAriaLabel();
-      expect(c1.getAttribute('aria-label'), 'Batman');
-
-      Polymer.dom(c1).text = 'Robin';
-      c1.updateAriaLabel();
-      expect(c1.getAttribute('aria-label'), 'Robin');
-    });
   });
 
   group('a11y', () {
     PaperCheckbox c1;
     PaperCheckbox c2;
 
     setUp(() {
       c1 = fixture('NoLabel');
       c2 = fixture('WithLabel');
     });
 
     test('has aria role "checkbox"', () {
       expect(c1.getAttribute('role'), equals('checkbox'));
       expect(c2.getAttribute('role'), equals('checkbox'));
     });
 
     test('checkbox with no label has no aria label', () {
-      expect(c1.getAttribute('aria-label'), isEmpty);
-    });
-
-    test('checkbox with a label sets an aria label', () {
-      expect(c2.getAttribute('aria-label'), equals("Batman"));
+      expect(c1.getAttribute('aria-label'), isNull);
     });
 
     test('checkbox respects the user set aria-label', () {
       PaperCheckbox c = fixture('AriaLabel');
       expect(c.getAttribute('aria-label'), equals("Batman"));
     });
 
     // TODO(jakemac): Investigate these
     // a11ySuite('NoLabel');
     // a11ySuite('WithLabel');
     // a11ySuite('AriaLabel');
   });
 }