Added version field to state and migrate from unversioned data State in older format must be migrated to new one. BUG:24869252 Change-Id: Iacadd1efb9e45e840b029652f8582d815ae0380e Reviewed-on: https://weave-review.googlesource.com/1305 Reviewed-by: Vitaly Buka <vitalybuka@google.com>