That link seems of mimimal value...It's a link to a conversation with a link to a bug about clarifying timeout.  I'm not seeing any problem description, or spec there.

It's a link to a pull request that adds a testcase to web-platform-tests for the problem seen in Chrome (and not in other browsers).

http://w3c-test.org/XMLHttpRequest/timeout-multiple-fetches.html

Note that it's flaky.

Flaky in Chrome or flaky due to a bug in the test? The Chrome web-platform-tests bot did not detect flaky behavior...

Flaky in Chrome, likely due to Chrome, but I'm not sure.

The flakiness comes from the network condition: Sometimes the preflight takes more than 1 sec and that results in timeout (i.e., PASS)

That is a long time for accessing localhost. I guess the only way to protect against that would be to make the timeout much larger and the delay on the server too.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a299a05414fc647524bf1da64fa2b058e5915d69

commit a299a05414fc647524bf1da64fa2b058e5915d69
Author: yhirano <yhirano@chromium.org>
Date: Mon Mar 27 09:12:43 2017

Stop having separate timeout timers for the preflight and the actual request

DocumentThreadableLoader stops the timeout timer and restarts it with fresh
timeout when getting a preflight response and sending the actual request. This
fixes it so that the timeout is applied to the combined request, not to each of
the preflight and the actual request.

BUG= 699985 
R=tyoshino@chromium.org

Review-Url: https://codereview.chromium.org/2755483006
Cr-Commit-Position: refs/heads/master@{#459728}

[add] https://crrev.com/a299a05414fc647524bf1da64fa2b058e5915d69/third_party/WebKit/LayoutTests/http/tests/xmlhttprequest/cross-origin-preflight-timeout.html
[add] https://crrev.com/a299a05414fc647524bf1da64fa2b058e5915d69/third_party/WebKit/LayoutTests/http/tests/xmlhttprequest/resources/access-control-allow-with-delay.php
[modify] https://crrev.com/a299a05414fc647524bf1da64fa2b058e5915d69/third_party/WebKit/Source/core/loader/DocumentThreadableLoader.cpp