Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/custom/element_upgrade_test.dart

 // Copyright (c) 2014, 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 register_element_proxy_test;
-
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
-import 'package:unittest/html_config.dart';
-import 'package:unittest/unittest.dart';
+
+import 'package:expect/minitest.dart';
+
 import '../utils.dart';
 
 class FooElement extends HtmlElement {
   static final tag = 'x-foo';
 
   final int initializedField = 666;
   js.JsObject _proxy;
 
   factory FooElement() => new Element.tag(tag);
   FooElement.created() : super.created() {
     _proxy = new js.JsObject.fromBrowserObject(this);
   }
 
   String doSomething() => _proxy.callMethod('doSomething');
 
   bool get fooCreated => _proxy['fooCreated'];
 }
 
 main() {
-  useHtmlConfiguration();
-
   var registered = false;
   var upgrader;
   setUp(() => customElementsReady.then((_) {
     if (!registered) {
       registered = true;
       upgrader = document.createElementUpgrader(FooElement);
       js.context['upgradeListener'] = (e) {
         upgrader.upgrade(e);
       };
 
@@ skipping 80 matching lines @@
 }
 
 class CustomDiv extends DivElement {
   CustomDiv.created() : super.created();
 }
 
 class CustomElement extends HtmlElement {
   factory CustomElement() => document.createElement('custom-element');
   CustomElement.created() : super.created();
 }