cumulative parameter will contain the total number of bytes received
thus far. If the response has been gzipped, this number will be the number
of compressed bytes that have been received across the wire.
total parameter will contain the expected total number of bytes to
be received across the wire (extracted from the value of the
Content-Length HTTP response header), or null if the size of the response
body is not known in advance (this is common for HTTP chunked transfer
encoding, which itself is common when a large amount of data is being
returned to the client and the total size of the response may not be known
until the request has been fully processed).
This is used in consolidateHttpClientResponseBytes.
typedef BytesReceivedCallback = void Function(int cumulative, int total);