[css-pseudo] Expose ::marker pseudo-element in devtools tree (back end)

If an element has a ::marker pseudo-element, it should be exposed in the
Elements panel, just like the ::before and ::after pseudo-elements.

This patch handles the back end part of that.

Bug: 457718


Change-Id: I80779dbc4171f54d3f7995e8aa46e284529a4178
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1934340
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#724122}
5 files changed