Add reference to invalid typedef so dart2js will detect it.

R=floitsch@google.com

Review URL: https://codereview.chromium.org/2417223002 .

tests/language/named_parameters_default_eq_test.dart

@@ -32,6 +32,9 @@ class A {
 }
 
 main() {
+  // Reference the type, or dart2js won't see that the declaration is invalid
+  F1 _ = null;  /// 01: continued
+
   var a = new A();
 
   int local({x = 3, y : 5, z}) => x * y * (z ?? 2);