“What was this building before?” is Howard Cushing’s favorite question. That’s because this patrician, shingled white building facing Newport harbor fits in so completely with the other buildings in this Rhode Island town known for its 18th century houses but also for sailing and society socializing. Though Cushing has a history in Newport as a descendant of a prominent family that includes the artist Howard Gardiner Cushing, his great grandfather, the building doesn’t: it’s a new build created by Cushing and partner Wirt Blaffer. But as Gardiner House, a boutique hotel that soft opened in September, it feels immediately in sync with Gilded Age grandeur-just with contemporary style.