SkPdfTree SkPdfStructureTreeRootDictionary::getIDTreeAsTree(SkPdfNativeDoc* doc) {
  SkPdfNativeObject* ret = get("IDTree", "");
  if (doc) {ret = doc->resolveReference(ret);}
  if ((ret != NULL && false) || (doc == NULL && ret != NULL && ret->isReference())) return ret->treeValue();
  // TODO(edisonn): warn about missing default value for optional fields
  return SkPdfTree();
}