Returns this DateTime value in the UTC time zone.
Returns this if it is already in UTC.
Otherwise this method is equivalent to:
new DateTime.fromMicrosecondsSinceEpoch(microsecondsSinceEpoch,
isUtc: true)
Source
DateTime toUtc() {
if (isUtc) return this;
return new DateTime._withValue(_value, isUtc: true);
}