Cleanup JS() expressions. New Constructor for JsObject that preserves the correct prototype. Type c…

tests/html/js_test.dart

Index: tests/html/js_test.dart
diff --git a/tests/html/js_test.dart b/tests/html/js_test.dart
index 7a0abbbbfd9cfafba84794a71601f19dfce387db..d4294168001eb555fcdc573eae0831e9fbf27efc 100644
--- a/tests/html/js_test.dart
+++ b/tests/html/js_test.dart
@@ -328,8 +328,9 @@ main() {
   test('js instantiation : >10 parameters', () {
     final o = new JsObject(context['Baz'], [1,2,3,4,5,6,7,8,9,10,11]);
     for (var i = 1; i <= 11; i++) {
-      o["f$i"] = i;
+      expect(o["f$i"], i);
     }
+    expect(o['constructor'], same(context['Baz']));
   });
 
   test('write global field', () {