anchor.diff:  import '../../pkg/unittest/lib/html_individual_config.dart';
   import 'dart:html';
   
  -class CustomType extends HtmlElement {
  +class CustomMixin {
  +  var mixinMethodCalled;
  +
  +  void mixinMethod() {
  +    mixinMethodCalled = true;
  +  }
  +}
  +
  +class CustomType extends HtmlElement with CustomMixin{
     factory CustomType() => null;
     bool onCreatedCalled; // = false;
     void onCreated() {
       onCreatedCalled = true;
       customCreatedCount++;
     }
  +
  +  void invokeMixinMethod() {
  +    mixinMethod();
  +  }
   }
   
   int customCreatedCount = 0;
  +
  +int nextTagId = 0;
  +String get nextTag => 'x-type${nextTagId++}';
   
   class NotAnElement {}
   
  
positive.code:     });
  
      test('query id', () {
        document.register('x-type9', CustomType);
        var element = new DivElement();
        element.innerHtml = '<x-type9 id="someid"></x-type9>';
        document.body.nodes.add(element);
        var queried = query('#someid');
  
  
negative.code:   group('preregister', () {
      // TODO(vsm): Modify this test once we agree on the proper semantics.
      test('pre-registration construction', () {
        var tag = nextTag;
        var dom = new Element.html('<div><$tag></$tag></div>');
        var preElement = dom.children[0];
        expect(preElement, isNotNull);
        expect(preElement is UnknownElement, isTrue);
  