What steps will reproduce the problem?
(1) Launch Chrome with --site-per-process or --isolate-origins=https://csreis.github.io and a clean profile
(2) Navigate to https://csreis.github.io
(3) Open DevTools
(4) Click Go cross-site (simple page)
(5) Observe original iframe content under its node (#document, etc).
Comment 1 by lukasza@chromium.org
, Jan 10 2018