Remove uses of unittest in the HTML tests where possible.

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

Index: pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart
diff --git a/pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart b/pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart
index c3ac8d9509087f7ee612cc0e1f3b041276b8bed3..4e9252de12cfdf7a280d454b4984f500481f8946 100644
--- a/pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart
+++ b/pkg/dev_compiler/test/codegen/lib/html/shadowroot_test.dart
@@ -2,14 +2,11 @@
 // 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';
 
-main() {
-  useHtmlConfiguration();
+import 'package:expect/minitest.dart';
 
+main() {
   var isShadowRoot =
       predicate((x) => x is ShadowRoot, 'is a ShadowRoot');