All CSV chunks joined in arrival order, typed with the meta frame's content type
or text/csv. Empty when the chunks went to ExportStreamOptions.onChunk
instead (see streamed).
File name from the meta frame, else the request's download_name, else
labjack_export.csv.
Requested channels with no rows in the range, from the summary frame, else empty.
Size in bytes: bytesSent from the summary frame, else the bytes received.
true when every chunk was handed to ExportStreamOptions.onChunk and not
kept, so blob is empty; false when blob holds the CSV.
Finished export assembled from the exporter's reply frames.