Support runtime check of function types.

tests/language/function_subtype_null.dart

+// Copyright (c) 2013, 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.
+// Dart test program for constructors and initializers.
+
+// Check function subtyping for null.
+
+import 'package:expect/expect.dart';
+
+typedef int Foo(bool a, [String b]);
+typedef int Bar<T>(T a, [String b]);
+
+main() {
+  Expect.isFalse(null is Foo, 'null is Foo');
+  Expect.isFalse(foo is Bar<bool>, 'foo is Bar<bool>');

[karlklose, 2013/06/21 12:48:41]

What is foo? 

[Johnni Winther, 2013/06/21 13:32:21]

Should be null.

+  Expect.isFalse(foo is Bar, 'foo is Bar');
+}