message: selection list box keydown function
diff: @@ -415,6 +415,7 @@ export interface ISelectionListBox {
  items(): Item[];
  getSelectedKey(): string;
  getSelectedItem(): Item;
  + keydown(e: KeyboardEvent);
  }
  export function selectionListBoxCreate(
  @@ -440,6 +441,7 @@ export function selectionListBoxCreate(
  listContainer.style.visibility = "hidden";
  },
  items: () => items,
  + keydown,
  nextItem,
  prevItem,
  removeHighlight,
  @@ -489,6 +491,14 @@ export function selectionListBoxCreate(
  }
  }
  + function keydown(e: KeyboardEvent) {
  + if (e.keyCode === KeyCode.upArrow) {
  + prevItem();
  + } else if (e.keyCode === KeyCode.downArrow) {
  + nextItem();
  + }
  + }
  +
  function init() {
  listContainer.style.boxShadow = "0px 3px 2px #bbbbbb";
  listContainer.style.backgroundColor = "white";
  