Begins asynchronously performing a DNS lookup for the given rrname, and eventually calls callback, which must
call lookup_records_async.end to get the final result.
See lookup_records for more details.
| this |
a Resolver |
| rrname |
the DNS name to lookup the record for |
| record_type |
the type of DNS record to lookup |
| cancellable |
a Cancellable, or null |
| callback |
callback to call after resolution completes |
| user_data |
data for |