The Whitney Museum is set to undergo a major transformation, as its board voted Tuesday to begin construction on a building in the Meatpacking District that will be completed in 2015. The board also has decided to sell a group of brownstones next to the museum’s Marcel Breuer-designed building on the Upper East Side, which means the art museum will almost certainly not be expanding in its current area. Since it is unlikely the museum will have the income to maintain two buildings, it is not clear what will happen to the Breuer building; one possibility floated by the Times is that it might be shared temporarily with another institution, like the Met. The Whitney’s chairman emiritus Leonard Lauder had been against the move, but changed his mind, seemingly taken - like a wide-eyed twentysomething new to the city - with the freshness of downtown: “Downtown is a new city, a new nation,†he said. “Why shouldn’t the Whitney be the museum of record there?â€