code: private boolean isObjectTypeWithNonStringifiableKey(JSType type) {
      if (!type.isTemplatizedType()) {
        return false;
      }
      TemplatizedType templatizedType = type.toMaybeTemplatizedType();
      if (templatizedType.getReferencedType().isNativeObjectType()
          && templatizedType.getTemplateTypes().size() > 1) {
        return !isReasonableObjectPropertyKey(templatizedType.getTemplateTypes().get(0));
      } else {
        return false;
      }
    }
docs: Checks whether current type is Object type with non-stringifable key.