isSafariIOS function
Implementation
bool isSafariIOS() {
var safariIOS = _safariIOS;
if (safariIOS != null) return safariIOS;
var userAgent = window.navigator.userAgent.toLowerCase();
safariIOS = userAgent.contains('safari') &&
RegExp(r'ip(?:ad|od|hone)').hasMatch(userAgent);
_safariIOS = safariIOS;
return safariIOS;
}