Introduce class TypeRef in the VM to fully support recursive types.

tests/language/cyclic_type_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.
+
+// Tests self referencing types.
+
+import "package:expect/expect.dart";
+
+class Base<T> {
+  get t => T;
+}
+
+class Derived<T> extends Base<Derived<Derived<T>>> {}
+
+class Derived1<T> extends Base<Derived2<T>> {}
+
+class Derived2<T> extends Base<Derived1<Derived2<T>>> {}
+
+main() {
+  var d = new Derived();
+  Expect.equals("Derived<Derived>", d.t.toString());
+  d = new Derived<bool>();
+  Expect.equals("Derived<Derived<bool>>", d.t.toString());
+  d = new Derived<Derived>();
+  Expect.equals("Derived<Derived<Derived>>", d.t.toString());
+  d = new Derived1();
+  Expect.equals("Derived2", d.t.toString());
+  d = new Derived2();
+  Expect.equals("Derived1<Derived2>", d.t.toString());
+  d = new Derived2<Derived1<int>>();
+  Expect.equals("Derived1<Derived2<Derived1<int>>>", d.t.toString());
+}