In a saucepan of boiling salted water blanch the sugar snap peas for 30 seconds, or until crisp-tender. Drain and refresh them under cold water. In a skillet, heat the butter over moderate heat until hot but not smoking. Add the shallots and cook, stirring, until softened. Add the peas, tomatoes, and salt and pepper and cook, stirring, until heated through. Stir in the chives.