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ARC data snapshots must be expired in 30 days if not updated.
Added timer to SnapshotInfo and tests.

BUG=b:161221001
TEST=components_unittests

Change-Id: If5cffeeba0957a0e5e9225c835241ec47a486c3e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2502690
Commit-Queue: Polina Bondarenko <pbond@chromium.org>
Auto-Submit: Polina Bondarenko <pbond@chromium.org>
Reviewed-by: Oleksandr Peletskyi <peletskyi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845260}