URL had properly named replacements for protocol(), set_protocol() and
create_with_file_protocol() already. This patch removes these function
and updates all call sites to use the functions named according to the
specification.
See https://url.spec.whatwg.org/#concept-url-scheme
If the request is stopped RequestServer::did_finish_request() will crash
on the VERIFY() call since request.total_size.has_value() returns false.
Let us instead use a conditional expression to verify if it has a value
and then call async_request_finished().
