private static ClusterState buildModifiedClusterState(ClusterState sourceState, DatabaseHandler.DatabaseContext dbContext) {
        ClusterState newState = sourceState.clone();
        for (NodeInfo n : dbContext.getCluster().getNodeInfos()) {
            NodeState ns = newState.getNodeState(n.getNode());
            if (!n.isDistributor() && ns.getStartTimestamp() == 0) {
                ns.setStartTimestamp(n.getStartTimestamp());
                newState.setNodeState(n.getNode(), ns);
            }
        }
        return newState;
    }
Checks if all distributor nodes have ACKed (and activated) the most recent cluster state.
Iff this is the case, triggers handleAllDistributorsInSync() on the provided FleetController
object and updates the broadcaster's last known in-sync cluster state version.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/SystemStateBroadcaster.java