[bedrock] Do not notify paint-as-active changes for closed Widgets

After a Widget has closed state in Widget and Widget subclasses may
have already undergone destruction.

To mitigate the risk of UAFs and access to partially destroyed
Widget state no-op paint-as-actve changes.

Bug: 413168662
Change-Id: Ib3faac6149cbc36a4cd5896a7c8aab059ab17c4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6856981
Reviewed-by: Fred Shih <ffred@chromium.org>
Commit-Queue: Tom Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1503155}