Support runtime check of function types.

tests/language/function_subtype_inline1_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.
+
+import 'package:expect/expect.dart';
+
+class A {}
+class B extends A {}
+class C extends A {}
+
+class Class<K,V> {
+  void forEach(void f(K k, V v)) {}
+}
+
+main() {
+  Class<B,C> c = new Class<B,C>();
+  c.forEach((A a, A b) {});
+  c.forEach((B a, C b) {});
+  try {
+    c.forEach((A a, B b) {});
+    Expect.isFalse(isCheckedMode());
+  } catch (e) {
+    Expect.isTrue(isCheckedMode());
+  }
+}
+
+
+isCheckedMode() {
+  try {
+    var i = 1;
+    String s = i;
+    return false;
+  } catch (e) {
+    return true;
+  }
+}