[Reland 2] Add TabFeatures and test harness for mocking out tab-based...

The first two attempts to land this CL were reverted not due to any
problem with the CL itself, but because a dependent CL introduced
flakiness. The flakiness has been diagnosed as a larger issue affecting
UI tests in general, see https://crbug.com/331859922. This may take time
to resolve.

This CL decouples itself from the dependent CL, thereby avoiding the
test flakiness issue.

> This reland has no change (other than a rebase) from the original CL. A
> precursor CL introduced flakiness to a test, which has since been fixed.
>
> > Add TabFeatures and test harness for mocking out tab-based features.
> >
> > This CL also hooks up the plumbing for LensOverlayController to
> > demonstrate how it would be used.
> >
> > Change-Id: I24c549da829d6953b4069a64e41dfe948218cefc
> > Reviewed-on:
> https://chromium-review.googlesource.com/c/chromium/src/+/5394701


> > Reviewed-by: David Pennington <dpenning@chromium.org>
> > Commit-Queue: Erik Chen <erikchen@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1278704}
>
> Bug: 331114227
> Change-Id: I27466e50f3370a130824e34179a7e1b17741f4d8
> Reviewed-on:
> https://chromium-review.googlesource.com/c/chromium/src/+/5400458


> Reviewed-by: David Pennington <dpenning@chromium.org>
> Commit-Queue: Erik Chen <erikchen@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1279332}

Change-Id: Ib898b57d59c29f5a6347de866cc5adbdde222c6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406084


Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Duncan Mercer <mercerd@google.com>
Cr-Commit-Position: refs/heads/main@{#1280329}