Depends on resolving the github issue in the description.

(The resolution happened)

Intent to Ship: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/gYrR2nR6quI

https://chromium-review.googlesource.com/c/chromium/src/+/1251421

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/029fb972512a6622bd5fe7aab30f932f3794f3fb

commit 029fb972512a6622bd5fe7aab30f932f3794f3fb
Author: Rune Lillesveen <futhark@chromium.org>
Date: Mon Oct 08 13:54:32 2018

Correct specificity for ::slotted() selectors.

Include specificity for compound inside ::slotted().

Intent to ship:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/gYrR2nR6quI

Bug:  888042 
Change-Id: Ibe421ce7423ba797cafd354696ff5cf693c52697
Reviewed-on: https://chromium-review.googlesource.com/c/1251421
Reviewed-by: Emilio Cobos Álvarez <emilio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597551}
[modify] https://crrev.com/029fb972512a6622bd5fe7aab30f932f3794f3fb/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/029fb972512a6622bd5fe7aab30f932f3794f3fb/third_party/blink/renderer/core/css/selector_checker.cc