Modified unittest to use new argument syntax.

tests/html/unknownelement_test.dart

Index: tests/html/unknownelement_test.dart
===================================================================
--- tests/html/unknownelement_test.dart	(revision 14114)
+++ tests/html/unknownelement_test.dart	(working copy)
@@ -17,8 +17,8 @@
   document.body.nodes.addAll([foo, bar]);
 
   test('type-check', () {
-      expect(foo is UnknownElement, isTrue);
-      expect(bar is UnknownElement, isTrue);
+      expect(foo, new isInstanceOf<UnknownElement>('UnknownElement'));
+      expect(bar, new isInstanceOf<UnknownElement>('UnknownElement'));
       expect(query('#foo'), equals(foo));
       expect(query('#bar'), equals(bar));
     });