Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart

 // Copyright (c) 2012, 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 ShadowRootTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html';
 
+import 'package:expect/minitest.dart';
+
 main() {
-  useHtmlConfiguration();
-
   var isShadowRoot =
       predicate((x) => x is ShadowRoot, 'is a ShadowRoot');
 
   test('ShadowRoot supported', () {
     var isSupported = ShadowRoot.supported;
 
     // If it's supported, then it should work. Otherwise should fail.
     if (isSupported) {
       var div = new DivElement();
       var shadowRoot = div.createShadowRoot();
       expect(shadowRoot, isShadowRoot);
       expect(div.shadowRoot, shadowRoot);
     } else {
       expect(() => new DivElement().createShadowRoot(), throws);
     }
   });
 }