Review

class ObjectType {
  /**
   * We treat this as the unknown type if any of its implicit prototype
   * properties is unknown.
   */
  @Override
  public boolean isUnknownType() {
    // If the object is unknown now, check the supertype again,
    // because it might have been resolved since the last check.
    if (unknown) {
      ObjectType implicitProto = getImplicitPrototype();
      if (implicitProto == null ||
          implicitProto.isNativeObjectType()) {
        unknown = false;
      } else {
        unknown = implicitProto.isUnknownType();
      }
    }
    return unknown;
  }

}