[Sync:USS] Implement cryptographer sync for keystore Nigori

Bug: 922900
Change-Id: I61d54db699e00a99ddbbcc95a6516411ab520ee0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1552806
Commit-Queue: Maksim Moskvitin <mmoskvitin@google.com>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653568}
4 files changed