Filed https://github.com/WICG/feature-policy/issues/241

https://chromium-review.googlesource.com/c/chromium/src/+/1329791

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59b93fee3639bf638833521032d30823f5240c01

commit 59b93fee3639bf638833521032d30823f5240c01
Author: Mike West <mkwst@chromium.org>
Date: Tue Nov 13 09:17:03 2018

Enable Feature Policy control over setting  `document.domain`.

Intent: https://groups.google.com/a/chromium.org/d/msg/blink-dev/Ff6Ywg5vnh4/VbDH4X6wBQAJ
Explainer: https://github.com/WICG/feature-policy/issues/241
Spec PR: https://github.com/whatwg/html/pull/4170

Bug: 904351
Change-Id: I14c0c3c871a01017f9c2bcbe8ed41c7b26782e71
Reviewed-on: https://chromium-review.googlesource.com/c/1329791
Commit-Queue: Mike West <mkwst@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607530}
[add] https://crrev.com/59b93fee3639bf638833521032d30823f5240c01/third_party/WebKit/LayoutTests/external/wpt/html/browsers/origin/relaxing-the-same-origin-restriction/document_domain_feature_policy.tentative.sub.html
[modify] https://crrev.com/59b93fee3639bf638833521032d30823f5240c01/third_party/blink/common/feature_policy/feature_policy.cc
[modify] https://crrev.com/59b93fee3639bf638833521032d30823f5240c01/third_party/blink/renderer/core/dom/document.cc
[modify] https://crrev.com/59b93fee3639bf638833521032d30823f5240c01/third_party/blink/renderer/core/feature_policy/feature_policy.cc

Nice!  Thanks for pushing forward with this!

I was under the impression that Feature Policy is document-wide rather than origin-wide, though.  Is that the case here?

If it's not origin-wide, then it's possible for another document in the same origin to still modify document.domain, and thus we wouldn't be able to safely use origin-level process isolation (as opposed to Site Isolation).  Would be great if I'm mistaken, though.  :)

creis@: This feature policy toggle is, indeed, document-centric. I don't think you'll be able to use it for origin-level process isolation until we're also shipping origin policy's feature-policy integration.

vogelheim@ has a behind-a-flag implementation of that up at https://chromium-review.googlesource.com/c/chromium/src/+/1202202. It would be great if y'all could collaborate with him to make sure the data can be exposed at whatever point during navigation you'll need it in order to make decisions about where to commit things.