Support runtime check of function types.

tests/language/function_subtype_cast2_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 casts.
+
+import 'package:expect/expect.dart';
+
+typedef void Foo<T>(T t);
+typedef void Bar(int i);
+
+class Class<T> {
+  test(bool expectedResult, var o, String typeName) {
+    if (expectedResult) {
+      Expect.isNotNull(o as Foo<T>, "bar as Foo<$typeName>");
+    } else {
+      Expect.throws(() => o as Foo<T>, (e) => true, "bar as Foo<$typeName>");
+    }
+    Expect.isNotNull(o as Bar, "bar as Bar");
+  }
+}
+
+void bar(int i) {}
+
+void main() {
+  new Class().test(true, bar, "dynamic");
+  new Class<int>().test(true, bar, "int");
+  new Class<bool>().test(false, bar, "bool");
+}