Shields panel doesn't always update immediately upon light/dark-mode toggle

Description

Shields panel doesn’t always update immediately upon light/dark-mode toggle

Steps to Reproduce

1. install 1.39.68
2. launch Brave
3. load twitch.tv
4. click on the Shields icon in the URL bar
5. in a new tab, open brave://settings/appearance
6. if Light, choose Dark, and vice-versa
7. in the twitch.tv tab, click again on the Shields icon in the URL bar

Actual result:

Expected result:

The Shields panel should observe pref changes to Light / Dark and re-validate its cache

Reproduces how often:

100%

Brave version (brave://version info)

Brave	1.39.68 Chromium: 101.0.4951.34 (Official Build) nightly (x86_64)
Revision	8f93af5d759634c5256b65997dedd138ed60992f-refs/branch-heads/4951@{#710}
OS	macOS Version 12.4 (Build 21F5048e)

cc @nullhook @rebron @MadhaviSeelam @GeetaSarvadnya

[simonhong]

This happens because shields bubble is destroyed after some delay. After some times passed(don’t know the exact timing…), shields bubble will have proper theme color. @nullhook Do you think shiels panel can monitor theme change and use it?

[stephendonner]

Verified PASSED using

Brave	1.41.77 Chromium: 103.0.5060.53 (Official Build) beta (64-bit)
Revision	a1711811edd74ff1cf2150f36ffa3b0dae40b17f-refs/branch-heads/5060@{#853}
OS	Linux

example	example	example