WASHINGTON — The Supreme Court’s recent decision to step into a relatively unimportant case involving Microsoft’s Xbox 360 gaming system revealed that Chief Justice John G. Roberts Jr. has sold between $250,000 and $500,000 in Microsoft stock in the past year.Federal judges violate the law if they take part in a case involving a company they own shares in, although Roberts declined through a court spokeswoman to comment on his situation.His decision, though, raises this question: If the chief justice can unload one of his …