Support runtime check of function types.

tests/language/function_subtype_local0_test.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 local functions.
+
+import 'package:expect/expect.dart';
+
+typedef int Foo(bool a, [String b]);
+typedef int Bar(bool a, [String b]);
+typedef int Baz(bool a, {String b});
+typedef int Boz(bool a);
+
+main() {
+  int foo(bool a, [String b]) => null;
+  int baz(bool a, {String b}) => null;
+  int boz(bool a, {int b}) => null;
+
+  Expect.isTrue(foo is Foo, 'foo is Foo');
+  Expect.isTrue(foo is Bar, 'foo is Bar');
+  Expect.isFalse(foo is Baz, 'foo is Baz');
+  Expect.isTrue(foo is Boz, 'foo is Boz');
+
+  Expect.isFalse(baz is Foo, 'baz is Foo');
+  Expect.isFalse(baz is Bar, 'baz is Bar');
+  Expect.isTrue(baz is Baz, 'baz is Baz');
+  Expect.isTrue(baz is Boz, 'baz is Boz');
+
+  Expect.isFalse(boz is Foo, 'boz is Foo');
+  Expect.isFalse(boz is Bar, 'boz is Bar');
+  Expect.isFalse(boz is Baz, 'boz is Baz');
+  Expect.isTrue(boz is Boz, 'boz is Boz');
+}