GitLab

This way embedders have API to know when they can take action
based on whether restore has completed.

BUG=1135278
TEST=covered by tests

Change-Id: I72d804a86d8c4eeafdc3b72bbcf16875a78eb477
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2451550
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814450}