V8 used to use the microtask context when it runs EnqueueJob
step 2.
> Let job settings be some appropriate environment settings object.
https://html.spec.whatwg.org/multipage/webappapis.html#enqueuejob(queuename,-job,-arguments)

However, it's being updated to use the handler's context.
https://github.com/whatwg/html/issues/1426#issuecomment-340071080

Change-Id: I24840a28ef2c903539fe4ace74ae59da290f5109
Reviewed-on: https://chromium-review.googlesource.com/c/1465902Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59870}