[css-pseudo] Expose ::marker styles in devtools

If an element has some styles for its ::marker pseudo-element, expose
them in the Styles panel when the element is inspected.

Bug: 1876407

TEST=http/tests/devtools/elements/elements-panel-styles.js

Change-Id: I56ab2703925966535beb71e0e47ab814c7ee07a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932447
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#724094}
4 files changed