Arianna Huffington is planting her flag — or at least a Post — in Chicago this summer. Reached last Friday in London, Huffington said she looked last week to finalize plans for a Chicago version of The Huffington Post Web site, the first of what the writer/Internet entrepreneur hopes will be dozens of localized news sites throughout the United States. “Chicago seemed a great city in which to test what we wanted to do [with] local around the country,” Huffington said. “It has everything … but wasn’t New York or L.A.”