Here is an explanation of the test regressions we encountered:

- These tests fail because the child frame now sees parent activation:
    external/wpt/fullscreen/api/element-ready-check-containing-iframe-manual.tentative.html
    external/wpt/html/user-activation/activation-api-iframe-no-activate.tenative.html
    fullscreen/full-screen-iframe-zIndex.html

- In these tests, security_origin->CanAccess() returns true from "127.0.0.1" to "localhost" domains.  For real cross-site domains, we confirmed the function returns false.
    http/tests/media/autoplay/document-user-activation-cross-origin-feature-policy-disabled.html
    http/tests/media/autoplay/document-user-activation-cross-origin-feature-policy-header.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc

commit 3b6636a484f810ebcc78b29f9cd7a5aebc4122fc
Author: Mustaq Ahmed <mustaq@google.com>
Date: Tue Jan 22 15:31:33 2019

New expectation file for not_site_per_process_webkit_layout_tests.

Bug: 922725
Change-Id: I057c6ee3839c51478eadfd1e27f0b03d356bce35
Reviewed-on: https://chromium-review.googlesource.com/c/1418519
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624786}
[modify] https://crrev.com/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc/testing/buildbot/chromium.fyi.json
[modify] https://crrev.com/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc/testing/buildbot/chromium.linux.json
[modify] https://crrev.com/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc/testing/buildbot/test_suites.pyl
[add] https://crrev.com/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc/third_party/blink/web_tests/FlagExpectations/disable-site-isolation-trials
[modify] https://crrev.com/3b6636a484f810ebcc78b29f9cd7a5aebc4122fc/third_party/blink/web_tests/TestExpectations