Reland "[Boca] Don't show notification when the caption is toggled off"

This is a reland of commit 1aa92aaaad99c813b1bcfada54355b73c6e1a221. The
revert was by mistake since the original CL was not the culprit for
flakiness.

Original change's description:
> [Boca] Don't show notification when the caption is toggled off
>
> Bug: b:408065504
> Change-Id: I6910761b510dce92d3daf653ac1087c2c9417c36
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6460774
> Reviewed-by: April Zhou <aprilzhou@google.com>
> Commit-Queue: Luke Cao <caott@google.com>
> Cr-Commit-Position: refs/heads/main@{#1447503}

Bug: b:408065504
Change-Id: Ied101495ca4aaf1dad6cb84fa1ab7bd3e4d99340
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6469246
Reviewed-by: Vignesh Shenvi <vshenvi@google.com>
Commit-Queue: Luke Cao <caott@google.com>
Cr-Commit-Position: refs/heads/main@{#1448657}