Update unittest to new package layout.

tests/html/audioelement_test.dart

 #library('AudioElementTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
+#import('../../pkg/unittest/lib/unittest.dart');
+#import('../../pkg/unittest/lib/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
   test('constructorTest1', () {
       var audio = new AudioElement();
       expect(audio, isNotNull);
       expect(audio is AudioElement);
     });
 
   test('constructorTest2', () {
       var audio = new AudioElement('hahaURL');
       expect(audio, isNotNull);
       expect(audio is AudioElement);
       expect(audio.src, contains('hahaURL'));
     });
 }