makeRequest abstract method
Similar to http2.ClientTransportConnection.makeRequest, but
handles connectring to the server and issuing the request.
Implementations can choose to manage the connections/streams however they see fit.
The uri is only used for establishing the socket connection
and any standard headers that can be derived from the uri
must be sent via headers, similar to what would be send to
http2.ClientTransportConnection.makeRequest.
Implementation
Future<http2.ClientTransportStream> makeRequest(
Uri uri,
List<http2.Header> headers,
);