Morgro Chemical Co., based in Salt Lake, has entered into an agreement with the Morton Salt division of Morton Thiokol Inc. to manufacture and market a de-icer compound, a Morgro spokesman said.Under the sublicense agreement, Morton Salt will manufacture and market a de-icer product using Propolyice(TM) - a patented ice-fighting compound for which Morgro holds the license. Morton Salt will test market the new product in major metropolitan areas during the 1988-89 winter season under the trademark Sidewalk Saver.