Fix result type checking of factory constructors of generic classes in VM.

tests/language/factory1_test.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.
+// Dart test program for testing factory generic result types.
+
+class A<T> {
+  A() { }
+  factory A.factory() {
+    return new A<String>();
+  }
+}
+
+class B<T> extends A<T> {
+  B() { }
+  factory B.factory() {
+    return new B<String>();
+  }
+}
+
+
+main() {
+  new A<String>.factory();
+  new A<int>.factory();  /// 00: dynamic type error
+  new B<String>.factory();
+  new B<int>.factory();  /// 01: dynamic type error
+}