Start cleaning up the HTML tests.

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

-library AudioElementTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
 import 'dart:html';
 
+import 'package:minitest/minitest.dart';
+
 main() {
-  useHtmlConfiguration();
-
   test('constructorTest1', () {
       var audio = new AudioElement();
       expect(audio, isNotNull);
       expect(audio is AudioElement, isTrue);
     });
 
   test('constructorTest2', () {
       var audio = new AudioElement('IntentionallyMissingFileURL');
       expect(audio, isNotNull);
       expect(audio is AudioElement, isTrue);
-      expect(audio.src, contains('IntentionallyMissingFileURL'));
+      expect(audio.src.contains('IntentionallyMissingFileURL'), isTrue);
     });
 
   test('canPlayTypeTest', () {
       var audio = new AudioElement();
       var canPlay = audio.canPlayType("audio/mp4");
       expect(canPlay, isNotNull);
       expect(canPlay is String, isTrue);
     });
 }