In a similar vein, I would very much like to modify the *status line* (e.g. "HTTP/1.0 200 OK") of responses in the webRequest.onHeadersReceived callback. The numeric part of the status line ('200')  is already exposed as a 'header' with key name 'status' but editing the value has no effect. 

It's true that the status line is NOT a header, as per RFC2616 (and subsequent RFCs), but modifying the status code in an extension could be very useful, e.g. for QA personnel looking to simulate internal errors on the server to trigger behavior in the front-end.

This bug is for tracking work to port existing WebRequest API features to new networking architecture in Chrome.

I think it's unlikely that we'd implement the feature you're requesting in c#2, but if you would like to request it, you should file a Feature Request at https://crbug.com/new rather than posting a comment here.

My thinking was that such a modification would require being done at a similar time and place as this bug; plus, as is so often the case with large, popular projects, creating new tickets is often an invitation to be told "that ticket already exists, stop wasting our time." So, this is a refreshing change, and I will do it.

this is for investigation only. Not blocking canary for now.