Keep a trail while checking upper bounds in the VM in order to properly handle

tests/language/regress_25568_test.dart

+// Copyright (c) 2016, 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.
+
+main() {}
+
+class BacklogListEditorState
+    extends AbstractListEditorState<BacklogsState, BacklogListEditorState> {}
+
+class BacklogsState extends MutableEntityState<BacklogsState> {}
+
+abstract class AbstractListEditorState<ES extends ComponentState<ES>,
+    S extends AbstractListEditorState<ES, S>> extends ComponentState<S> {}
+
+abstract class ComponentState<S extends ComponentState<S>> {}
+
+abstract class EntityState<ES extends EntityState<ES>>
+    extends ComponentState<ES> {}
+
+abstract class MutableEntityState<S extends MutableEntityState<S>>
+    extends EntityState<S> implements ComponentState<S> {}
+