src/language-js/printer-estree.js/isFlowAnnotationComment
function isFlowAnnotationComment(text, typeAnnotation, options) {
  const start = options.locStart(typeAnnotation);
  const end = privateUtil.skipWhitespace(text, options.locEnd(typeAnnotation));
  return text.substr(start, 2) === "/*" && text.substr(end, 2) === "*/";
}