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- Add more accessible labels for title and alert states.
- Move the focusable target from TabElement's host to inner #tab
element to allow aria-labelledby to work.
- Add role and tabindex to appropriate elements.
- Does not update focus outline UI.

Screenshot examples of what is read out: https://imgur.com/a/o0Hmu3a

Bug: 1017472
Change-Id: I230e810fadf92749c2ecf824bb92eb4d8c45774d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1877194
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709246}