Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/custom/document_register_basic_test.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 document_register_basic_test;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html';
+
+import 'package:expect/minitest.dart';
+
 import '../utils.dart';
 
 class Foo extends HtmlElement {
   static final tag = 'x-foo';
   factory Foo() => new Element.tag(tag);
   Foo.created() : super.created();
 
   get thisIsACustomClass => true;
 }
 
@@ skipping 19 matching lines @@
 abstract class BadC extends HtmlElement {
   BadC.created() : super.created();
 }
 
 class BadF implements HtmlElement {
   static final tag = 'x-tag-f';
   factory BadF() => new Element.tag(tag);
 }
 
 main() {
-  useHtmlConfiguration();
-
   // Adapted from Blink's fast/dom/custom/document-register-basic test.
 
   setUp(() => customElementsReady);
 
   test('Testing document.registerElement() basic behaviors', () {
     document.registerElement(Foo.tag, Foo);
 
     // Cannot register an existing dart:html type.
     expect(() => document.registerElement('x-bad-a', HtmlElement), throws);
 
@@ skipping 79 matching lines @@
     expect(container.firstChild.tagName, "X-BAR");
     expect(container.lastChild is Bar, isTrue);
     expect(container.lastChild.tagName, "X-BAR");
 
     // Constructors shouldn't interfere with each other
     expect((new Foo()).tagName, "X-FOO");
     expect((new Bar()).tagName, "X-BAR");
     expect((new Baz()).tagName, "X-BAZ");
   });
 }