TIER REIT — the developer bent on turning The Domain into Austin's next downtown-like office market — is blazing ahead with new construction and said it’s close to inking significant leases for yet another skyscraper there. It’s also almost fully leased Third + Shoal downtown, Facebook's new local headquarters. The social media giant already had the lion's share of the building — its second downtown tower here to occupy — but it just ordered up space for another hundred or so employees.