The swiftness of the changes in Saudi Arabia has residents long used to its sleepy social life blinking in shock, like Dorothy stepping out of her sepia-toned Kansas house into Technicolor Oz. December’s calendar alone featured Balad Beast, the Red Sea International Film Festival, the Dakar Rally, the Riyadh Season — a monster lineup of concerts and sporting events — and the Boulevard Riyadh, a sort of world fair in the Saudi capital with pavilions showcasing foreign countries, including the U.S., which was represented by a chunk of interstate highway asphalt, a Magnolia Bakery and a police cruiser.