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This CL also removes some accessibility features as tabs are not
focusable only through the keyboard, and overall accessibility is still
being decided on.

Bug: 989131
Change-Id: I4aae2fd35000866dca0c641ce59c93a05e191a3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1747732Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686215}