Add reference to invalid typedef so dart2js will detect it.

tests/language/named_parameters_default_eq_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Check that both `=` and `:` are allowed for named parameters.
 
 import "package:expect/expect.dart";
 
 // Default values are not allowed on typedefs.
 typedef int F1({x = 3, y}); /// 01: compile-time error
@@ skipping 14 matching lines @@
   // Default values are not allowed on redirecting factory constructors.
   factory A.badRedirectFactory({x = 3, y}) = A; /// 02: compile-time error
 
   int get value => x * y * z;
 
   static int staticF({x = 3, y : 5, z}) => x * y * (z ?? 2);
   int instanceF({x = 3, y : 5, z}) => x * y * (z ?? 2);
 }
 
 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);
   var expr = ({x = 3, y : 5, z}) => x * y * (z ?? 2);
   var tearOff = a.instanceF;
 
   test(function) {
     Expect.equals(30, function());
     Expect.equals(70, function(x: 7));
     Expect.equals(42, function(y: 7));
@@ skipping 42 matching lines @@
 
   Expect.equals(30, new A.redirectFactory().value);
   Expect.equals(70, new A.redirectFactory(x: 7).value);
   Expect.equals(42, new A.redirectFactory(y: 7).value);
   Expect.equals(28, new A.redirectFactory(x: 7, y: 2).value);
   Expect.equals(15, new A.redirectFactory(z: 1).value);
   Expect.equals(21, new A.redirectFactory(y: 7, z: 1).value);
   Expect.equals(35, new A.redirectFactory(x: 7, z: 1).value);
   Expect.equals(14, new A.redirectFactory(x: 7, y: 2, z: 1).value);
 }