ContentSuggestions - restore snapshots when needed

Make ContentSuggestions restore snapshots from disk where needed.
Previously this wasn't needed as only the running task would be
used for content suggestions. Now it can be invoked for any task
in Overview so need to be able to restore snapshots from disk.

Bug: 149595462
Test: manual
Change-Id: Ia67efc122a44b27a9049e48afaf2ddb789bc31b9