Function updateClasses

test/angular/1.2/angular.js:18591–18604

(oldClasses, newClasses)

        }

        function updateClasses (oldClasses, newClasses) {
          var toAdd = arrayDifference(newClasses, oldClasses);
          var toRemove = arrayDifference(oldClasses, newClasses);
          toRemove = digestClassCounts(toRemove, -1);
          toAdd = digestClassCounts(toAdd, 1);

          if (toAdd.length === 0) {
            $animate.removeClass(element, toRemove);
          } else if (toRemove.length === 0) {
            $animate.addClass(element, toAdd);
          } else {
            $animate.setClass(element, toAdd, toRemove);
          }
        }

        function ngClassWatchAction(newVal) {
          if (selector === true || scope.$index % 2 === selector) {