Replace tab strip observer from chip view

First step in cleaning up the relationship between these classes.
In moving this logic to the tab helper, it is being migrated from
a TabStripModelObserver to using WebContentsObserver to check
visibility changes. When a previously visible tab is hidden then the
boolean gets updated. This will be followed by subsequent CLs to
move more of the logic.

Bug: 1445979
Change-Id: Ia5feafb914a10739efeea76579eee1f9af8c2ec1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4563101
Commit-Queue: Alison Gale <agale@chromium.org>
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1149338}