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This is a reland of bb70008e

Original change's description:
> [Autofill Assistant] Add ShowProgressBar action.
> 
> Screenshot: https://screenshot.googleplex.com/chZ1byvKBqa.png
> 
> Bug: 806868
> Change-Id: Ib7714b1b554d030c461614bcd51cc30156cac594
> Reviewed-on: https://chromium-review.googlesource.com/c/1278808
> Reviewed-by: Theresa <twellington@chromium.org>
> Reviewed-by: Ganggui Tang <gogerald@chromium.org>
> Commit-Queue: Jordan Demeulenaere <jdemeulenaere@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#600015}

Bug: 806868
Change-Id: Ieb4d6c6305a155985fb3eabf80763d6d2e1b491d
Reviewed-on: https://chromium-review.googlesource.com/c/1284929Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Jordan Demeulenaere <jdemeulenaere@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600406}