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- Give error divs role=alert so that errors get announced.
- Make progress wheel accessible by setting role=progressbar and
  and providing progress via aria-valuenow. Set tabindex=0 during
  progress so that it can be focused and the percentage read.
- Add a label for the device name.
- Make the confirmation token an aria-live region so it gets read when
  it shows up.
- Hide the add contact section when the error section is visible to
  prevent overflow. (Add contact isn't implemented yet -- the elements
  are on the page, but they're never visible.)

Bug: 1148475
Change-Id: I49cbcb8c7930a3eddad042ce1ea5389306a6d067
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2569897Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: Curt Clemens <cclem@google.com>
Cr-Commit-Position: refs/heads/master@{#833745}