The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a5c7e067f550762c21fc76056fd3254f1c2ae8e

commit 7a5c7e067f550762c21fc76056fd3254f1c2ae8e
Author: Mike West <mkwst@chromium.org>
Date: Wed Jun 14 19:44:20 2017

Evaluate making `document.domain` nullable.

There might be a reasonable use case for nulling out `document.domain`
in order to prevent a document from being able to access the DOM of
other documents served from the same physical origin (by walking the
frame tree of its embedder, for example).

This patch implements `document.domain = null` behind the experimental
flag in order to determine whether or not it solves the problem without
unworkable side-effects. If so, I'll formalize
https://github.com/whatwg/html/issues/2757 into a real patch against
HTML for discussion/

Bug: 733150
Change-Id: Ic6906d17b6e8bcb1882408ac6152ae3dd6f8700a
Reviewed-on: https://chromium-review.googlesource.com/535536
Commit-Queue: Mike West <mkwst@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#479470}
[add] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/LayoutTests/external/wpt/html/browsers/origin/relaxing-the-same-origin-restriction/document_domain_setter_null.tentative.html
[add] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/LayoutTests/external/wpt/html/browsers/origin/relaxing-the-same-origin-restriction/document_domain_setter_srcdoc.html
[add] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/LayoutTests/external/wpt/html/browsers/origin/relaxing-the-same-origin-restriction/support/document_domain_frame.html
[modify] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/LayoutTests/http/tests/security/document-domain-invalid.html
[modify] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/Source/core/dom/Document.cpp
[modify] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
[modify] https://crrev.com/7a5c7e067f550762c21fc76056fd3254f1c2ae8e/third_party/WebKit/Source/platform/weborigin/SecurityOrigin.cpp