Add support for testing content in SkyView

sky/tests/framework/basic.sky

 <import src="../resources/run-after-display.sky" />
 <script>
-import 'basic.dart';
+import '../resources/dom_serializer.dart';
 import 'dart:sky';
-import '../resources/dom_serializer.dart';
 import 'dart:sky.internals' as internals;
+import 'resources/basic.dart';
 
 void main() {
   new TestApp();
   runAfterDisplay(() {
     document.firstChild.remove();
     document.firstChild.remove();
     var result = serializeNode(document);
     try {
       internals.notifyTestComplete(result);
     } catch (e) {
       print(e);
       print(result);
     }
   });
 }
 </script>