[TabGroup] Permit metadata getters by Tab to work while closing

Allow getters for title and color of a tab group to work via tab
for closing tab groups.

This allows the undo tab closure snackbar and recent tabs to work
without issue. Post tab collections this behavior can also work by
relying on detached tab groups to fetch this information.

Bug: 399354986
Change-Id: I497fb62ee6870cc5ca57bb374e9995c7f54e3cf3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6722855
Auto-Submit: Calder Kitagawa <ckitagawa@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Commit-Queue: Sky Malice <skym@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1485718}