Selector checker now matches classes from selector to classes
from pseudo-element.

The classes aren't saved on the pseudo-element, but rather in the
ViewTransitionStyleTracker, in the element map.

Bug: 1519997
Change-Id: Iee74bb5d8e6f1ced0edfbcdc1ac9eec32497e97f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5253451


Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Khushal Sagar <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1257975}