With regards to requests in the Network tab with the status "cancelled" - there is no default timeout on AJAX requests in Chrome/Chromium, however there are a few places where Chrome/Chromium will cancel a request:
the DOM element that caused the request to be made got deleted (i.e. an IMG is being loaded, but before the load happened, the IMG node was deleted)
something was done that made loading the data unnecessary. (i.e. started loading a iframe, then changed the src or overwrote the contents)
there are lots of requests going to the same server, and a network problem on earlier requests showed that subsequent requests weren't going to work (DNS lookup error, earlier (same) request resulted e.g. HTTP 400 error code, etc)
- this might also happen if you have a button that submit's the request wrapped in a form element, if
preventDefaultisn't called on the click event two request will be sent and result in the cancellation.