Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/track_element_constructor_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.
 
 // A regression test for dart2js generating illegal JavaScript code
 // dynamically in non-csp mode.  The name of the field "defaultValue"
 // in JavaScript is "default".  This meant that dart2js would create a
 // constructor function that looked like this:
 //
 // function TrackElement(default) { this.default = default; }
 
 import 'dart:html';
 
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
+import 'package:expect/minitest.dart';
 
 void main() {
-  useHtmlConfiguration();
   test('', () {
     if (!TrackElement.supported) return;
     document.body.append(new TrackElement()..defaultValue = true);
-    if (!document.query('track').defaultValue) {
+    var trackElement = document.query('track') as TrackElement;
+    if (!trackElement.defaultValue) {
       throw 'Expected default value to be true';
     }
-    document.query('track').defaultValue = false;
-    if (document.query('track').defaultValue) {
+    trackElement.defaultValue = false;
+    if (trackElement.defaultValue) {
       throw 'Expected default value to be false';
     }
   });
 }