Flaky abortsignal-timeout.html test due to incomplete implementation of run_steps_after_a_timeout_impl

[rcorsi]

Issue #6362 reported that the LibWeb test Text/input/abortsignal-timeout.html would randomly fail due to the expected 10ms timeout being detected as 9ms. In some rare cases the test has been seen to timeout at 7ms or 8ms.

Fix #6422 was put into place to solved most of the failures specifically when the 9ms timeout is detected.

During the investigation it was noted that the abort signal timeout is managed by the implementation of WindowOrWorkerGlobalScopeMixin::run_steps_after_a_timeout_impl() which is incomplete and has 8 FIXME statements.

See Libraries/LibWeb/HTML/WindowOrWorkerGlobalScope.cpp:1022

Specs are here: https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#run-steps-after-a-timeout

This is a followup issue to complete the implementation.

[rcorsi]

@gmta is this what you were looking for? Any additional information should be added to this issue?

[rcorsi]

At the creation of this issue, the top of master was 120bba5