Support runtime check of function types.

tests/language/function_subtype_call0_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 classes with call functions.
+
+import 'package:expect/expect.dart';
+
+typedef void Foo(bool a, [String b]);
+typedef void Bar(bool a, [String b]);
+typedef void Baz(bool a, {String b});
+typedef void Boz(bool a);
+
+class C1 {
+  void call(bool a, [String b]) {}
+}
+
+class C2 {
+  void call(bool a, {String b}) {}
+}
+
+class C3 {
+  void call(bool a, {int b}) {}
+}
+
+main() {
+  Expect.isTrue(new C1() is Foo, 'new C1() is Foo');
+  Expect.isTrue(new C1() is Bar, 'new C1() is Bar');
+  Expect.isFalse(new C1() is Baz, 'new C1() is Baz');
+  Expect.isTrue(new C1() is Boz, 'new C1() is Boz');
+
+  Expect.isFalse(new C2() is Foo, 'new C2() is Foo');
+  Expect.isFalse(new C2() is Bar, 'new C2() is Bar');
+  Expect.isTrue(new C2() is Baz, 'new C2() is Baz');
+  Expect.isTrue(new C2() is Boz, 'new C2() is Boz');
+
+  Expect.isFalse(new C3() is Foo, 'new C3() is Foo');
+  Expect.isFalse(new C3() is Bar, 'new C3() is Bar');
+  Expect.isFalse(new C3() is Baz, 'new C3() is Baz');
+  Expect.isTrue(new C3() is Boz, 'new C3() is Boz');
+}