[css-pseudo] Allow nested ::marker pseudo-elements

Currently, pseudo-elements can only be originated by elements. However,
::before or ::after pseudo-elements can have 'display: list-item', and
thus should be able to originate a nested ::marker.

This patch adds the changes for making that possible. But note it has
no effect in practice, since currently list markers are only pseudo-
elements when their 'content' is not 'normal', and a nested ::marker
can't be targeted by selectors yet.

However, this change is necessary for implementing 'content: normal'
markers as real pseudo-elements.


Change-Id: I81a5c90b7117127e251a296c0bef66a12a95129c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1995329
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#730531}
4 files changed