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

runtime/lib/type_patch.dart

 // Copyright (c) 2012, 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.
 
 // These Dart classes correspond to the VM internal implementation classes.
 
 // Equivalent of RawAbstractType.
 abstract class _AbstractType implements Type {
   String toString() native "AbstractType_toString";
 }
 
 // Equivalent of RawType.
 class _Type extends _AbstractType {
 }
 
+// Equivalent of RawTypeRef.
+class _TypeRef extends _AbstractType {
+}
+
 // Equivalent of RawTypeParameter.
 class _TypeParameter extends _AbstractType {
 }
 
 // Equivalent of RawBoundedType.
 class _BoundedType extends _AbstractType {
 }
 
 // Equivalent of RawMixinAppType.
 class _MixinAppType extends _AbstractType {
 }