Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/window_mangling_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 WindowManglingTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html' as dom;
 
+import 'package:expect/minitest.dart';
+
 // Defined in dom.Window.
 get navigator => "Dummy";
 
 $eq(x, y) => false;
 $eq$(x, y) => false;
 
 main() {
-  useHtmlConfiguration();
   var win = dom.window;
 
   test('windowMethod', () {
       final message = navigator;
       final x = win.navigator;
-      expect(x, isNot(equals(message)));
+      expect(x, notEquals(message));
     });
 
   test('windowEquals', () {
       expect($eq(win, win), isFalse);
       expect(win == win, isTrue);
     });
 
   test('windowEquals', () {
       expect($eq$(win, win), isFalse);
       expect(win == win, isTrue);
     });
 }