static unwrap(safeScript) {
    return SafeScript.unwrapTrustedScript(safeScript).toString();
  }
Performs a runtime check that the provided object is indeed a
SafeScript object, and returns its value.

@param {!SafeScript} safeScript The object to extract from.
@return {string} The safeScript 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.unwrapScript` combined with `.toString()`
    instead.