Complete latest spec changes regarding malformed types (see issue 14006).

tests/language/isnot_malformed_type_test.dart

Index: tests/language/isnot_malformed_type_test.dart
===================================================================
--- tests/language/isnot_malformed_type_test.dart	(revision 29871)
+++ tests/language/isnot_malformed_type_test.dart	(working copy)
@@ -5,10 +5,10 @@
 import 'package:expect/expect.dart';
 
 f(obj) {
-  // 'Baz' is not loaded, mapped to dynamic.
+  // 'Baz' is not loaded, malformed.
   return (obj is !Baz);
 }
 
 main () {
-  Expect.isFalse(f(null));
+  Expect.throws(() => f(null), (e) => e is TypeError);
 }