Support runtime check of function types.

tests/language/function_subtype_typearg0_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 with type variables in factory constructors.
+
+import 'package:expect/expect.dart';
+
+typedef void Foo();
+
+class A<T> {
+  bool foo(a) => a is T;
+}
+
+void bar1() {}
+void bar2(i) {}
+
+void main() {
+  void bar3() {}
+  void bar4(i) {}
+
+  Expect.isTrue(new A<Foo>().foo(bar1));
+  Expect.isFalse(new A<Foo>().foo(bar2));
+  Expect.isTrue(new A<Foo>().foo(bar3));
+  Expect.isFalse(new A<Foo>().foo(bar4));
+  Expect.isTrue(new A<Foo>().foo((){}));
+  Expect.isFalse(new A<Foo>().foo((i){}));
+}