Start cleaning up the HTML tests.

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

-library AudioBufferSourceNodeTest;
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_individual_config.dart';
 import 'dart:web_audio';
 
+import 'package:minitest/minitest.dart';
+
 main() {
-
-  useHtmlIndividualConfiguration();
-
   group('supported', () {
     test('supported', () {
-      expect(AudioContext.supported, true);
+      expect(AudioContext.supported, isTrue);
     });
   });
 
   group('functional', () {
     test('createBuffer', () {
-      if(AudioContext.supported) {
+      if (AudioContext.supported) {
         var ctx = new AudioContext();
         AudioBufferSourceNode node = ctx.createBufferSource();
         expect(node is AudioBufferSourceNode, isTrue);
         node.start(ctx.currentTime, 0, 2);
         expect(node is AudioBufferSourceNode, isTrue);
       }
     });
   });
 }