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Announce to screenreaders that a permission has requested if chip UI is
used. For prompt UI, the bubble is shown and it takes over the focus.
Chip UI is less intrusive so it must be explicitly announced for screen
reader users. To avoid users not hearing the announcement, it would be
reannouced after 2 minutes.

Chip UI is now one of the panes (users can cycle through panes with F6).
This way users can easily access it with keyboard which is very
important for screenreader users.

Also to make sure that users don't miss pending permission request,
added message about having pending permission request to tab
announcement.

Previous CL was revered here:
https://chromium-review.googlesource.com/c/chromium/src/+/2586966.

Bug: 1150836
Change-Id: Ic6a5dddb3368ad4ed90e33cefa7673df843f4b69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2624468
Commit-Queue: Olesia Marukhno <olesiamarukhno@google.com>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844528}