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Add a new rollback icon (vertically flipped update icon) and use it in
the rollback notification.

Screenshot: https://screenshot.googleplex.com/UebqEykm9P7.png

Bug: 863088
Change-Id: I45dea5daac43469349a0cccd166a6338532ce55f
Reviewed-on: https://chromium-review.googlesource.com/1145071Reviewed-by: Jenny Zhang <jennyz@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Marton Hunyady <hunyadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577023}