The old test also fails after making WebUI pages use origin locks (see https://crrev.com/c/1237392) so I'd also like to either remove the test.

Direct link to the CR comment quoted above: https://chromium-review.googlesource.com/c/chromium/src/+/1025673/23/content/browser/site_instance_impl_unittest.cc#690

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1f5ad409dbf5334523931df37598ea49e9849c87

commit 1f5ad409dbf5334523931df37598ea49e9849c87
Author: Lukasz Anforowicz <lukasza@chromium.org>
Date: Fri Sep 28 23:57:54 2018

Allow origin lock for WebUI pages.

Returning true for WebUI pages in DoesSiteRequireDedicatedProcess helps
to keep enforcing a SiteInstance swap during chrome://foo ->
chrome://bar navigation, even after relaxing
BrowsingInstance::GetSiteInstanceForURL to consider RPH::IsSuitableHost
(see https://crrev.com/c/783470 for that fixes process sharing in
isolated(b(c),d(c)) scenario).

I've manually tested this CL by visiting the following URLs:
- chrome://welcome/
- chrome://settings
- chrome://extensions
- chrome://history
- chrome://help and chrome://chrome (both redirect to chrome://settings/help)

Bug:  510588 ,  847127 
Change-Id: I55073bce00f32cb8bc5c1c91034438ff9a3f8971
Reviewed-on: https://chromium-review.googlesource.com/1237392
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595259}
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/chrome/browser/renderer_host/render_process_host_chrome_browsertest.cc
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/chrome/browser/resource_coordinator/tab_manager_browsertest.cc
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/content/browser/frame_host/render_frame_host_manager_browsertest.cc
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/content/browser/frame_host/webui_navigation_browsertest.cc
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/content/browser/site_instance_impl.cc
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/content/browser/site_instance_impl.h
[modify] https://crrev.com/1f5ad409dbf5334523931df37598ea49e9849c87/content/browser/site_instance_impl_unittest.cc