Chrome Version: 71.0.3578.98 (Official Build) (64-bit)
OS: all

I noticed this while working on issue #908926.

What steps will reproduce the problem?
(1) Open two windows.
(2) Load https://davidben.scripts.mit.edu/auth-test/1 in one window.
(3) Load https://davidben.scripts.mit.edu/auth-test/2 in the other. (different URLs is to work around issue #864572)
(4) Close the first tab

What is the expected result?
The second tab is unchanged.

What happens instead?
The second tab's prompt is dismissed. This also happens if the request is an XHR and the site aborts the request.

This is because the OnRequestCancelled flow still trips NotifyAuthCancelled, which is the code to deduplicate user responses to the auth prompts. But the request getting canceled isn't a user response.