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Add parsing/syncing to local state arc.snapshot pref of snapshot related info.
Add blocked UI mode Chrome start up along with clearing outdated
snapshots flow.
Currently, ArcDataSnapshotdManager functionality is disabled for testing.

BUG=b:161221001
TEST=components_unittests

Change-Id: I6ccfe44c3b85a6dc864914609fa41c071e81e4a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385396
Commit-Queue: Polina Bondarenko <pbond@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Auto-Submit: Polina Bondarenko <pbond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809390}