warn_warnNoMutationObserverSupport = function warnNoMutationObserverSupport(source) {
  /* istanbul ignore else */
  if (hasMutationObserverSupport) {
    return false;
  } else {
    warn_warn("".concat(source, ": Requires MutationObserver support."));
    return true;
  }
}
Warn when no MutationObserver support is given
@param {string} source
@returns {boolean} warned