Reland "[Extensions] Regression test: WebRequestAPI ResetURLLoaderFactories bug"

Test needs to be skipped when `kForceWebRequestProxyForTest` is enabled
(for example, in `network_service_linux` trybot).

That's because factories are never reset when this feature is enabled.

See
https://crsrc.org/c/extensions/browser/api/web_request/web_request_api.cc;drc=e1dda381f52e3a553444a434e89139e016675701;l=680

This is a reland of commit e1dda381f52e3a553444a434e89139e016675701

Original change's description:
> [Extensions] Regression test: WebRequestAPI ResetURLLoaderFactories bug
>
> This change adds a regression test for the referenced bug.
>
> It tests both that enabling the `DeferResetURLLoaderFactories` feature
> flag resolves the issue, and that disabling it causes the issue.
>
> Design doc: http://go/defer-reset-url-loader-factories
>
> Bug: 394523691
> Change-Id: I46671553e4c0631416b76654c476cb6e29dd65ae
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6424484
> Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
> Commit-Queue: Andrea Orru <andreaorru@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1443868}

Bug: 394523691
Change-Id: I21b26c9a60a470be52148a6c11de474b38a4b496
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6438674
Reviewed-by: Devlin Cronin <rdevlin.cronin@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Commit-Queue: Andrea Orru <andreaorru@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1444520}