code: static boolean isClassType(Element element, Elements elements, Types types) {
      TypeMirror classType = types.getDeclaredType(
          elements.getTypeElement(Class.class.getName()),
          types.getWildcardType(null, null));
      return types.isAssignable(element.asType(), classType);
    }
docs: Returns true if {@code element} is a {@link Class} type.