static unwrap(safeHtml) {
    return SafeHtml.unwrapTrustedHTML(safeHtml).toString();
  }
Performs a runtime check that the provided object is indeed a SafeHtml
object, and returns its value.
@param {!SafeHtml} safeHtml The object to extract from.
@return {string} The SafeHtml object's contained string, unless the
    run-time type check fails. In that case, `unwrap` returns an innocuous
    string, or, if assertions are enabled, throws
    `asserts.AssertionError`.
@deprecated Use `safevalues.unwrapHtml` combined with `toString()` instead.