The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1d064e771eff76425807c1efd3908b395954b453

commit 1d064e771eff76425807c1efd3908b395954b453
Author: Rune Lillesveen <futhark@chromium.org>
Date: Fri Nov 02 14:24:32 2018

Keep previous_in_flow across shadow boundary.

For some reason we created a new AttachContext entering a ShadowRoot for
AttachLayoutTree. If the shadow host was display:contents we would lose
the previous_in_flow from the shadow tree checking the need for
whitespace LayoutObject for shadow host siblings.

Created a common space-separated words expectation for css.

Bug:  901323 
Change-Id: Ib2fa54d55923c0497ff8e96c5010e68b01570881
Reviewed-on: https://chromium-review.googlesource.com/c/1314589
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604910}
[add] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/css-display/display-contents-shadow-host-whitespace.html
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/css-flexbox/anonymous-flex-item-001.html
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/css-flexbox/anonymous-flex-item-002.html
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/css-flexbox/anonymous-flex-item-003.html
[delete] https://crrev.com/d5a114b16d5abe7a59362b183fa06c83158c43a1/third_party/WebKit/LayoutTests/external/wpt/css/css-text/white-space/reference/white-space-empty-text-sibling-ref.html
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/css-text/white-space/white-space-empty-text-sibling.html
[rename] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/WebKit/LayoutTests/external/wpt/css/reference/pass_if_two_words.html
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/blink/renderer/core/dom/shadow_root.cc
[modify] https://crrev.com/1d064e771eff76425807c1efd3908b395954b453/third_party/blink/renderer/core/dom/shadow_root.h