code: function (classes) {
              this._classList = classes.split(' ').reduce(function (obj, className) {
                  obj[className] = true;
                  return obj;
              }, {});
              this.setPositionClasses(this.positionX, this.positionY);
          }
docs: This method takes classes set on the host md-menu element and applies them on the
  menu template that displays in the overlay container.  Otherwise, it's difficult
  to style the containing menu from outside the component.
  @param {?} classes list of class names
  @return {?}