This signal is emitted after [signal@Message:SoupMessage:got-headerss].
If content sniffing is disabled, or no content sniffing will be performed, due to the sniffer deciding to trust the Content-Type sent by
the server, this signal is emitted immediately after [signal@Message:SoupMessage:got-headerss], and type is
null.
| type |
the content type that we got from sniffing |
| params |
a GenericSet with the parameters |