message: Handle LEFT Arrow as expected by Aria Treeview Widget pattern
diff: @@ -133,6 +133,13 @@ const RoomSubList = createReactClass({
  // Prevent LeftPanel handling Tab if focus is on the sublist header itself
  ev.stopPropagation();
  break;
  + case Key.ARROW_LEFT:
  + // On ARROW_LEFT collapse the room sublist
  + if (!this.state.hidden && !this.props.forceExpand) {
  + this.onClick();
  + }
  + ev.stopPropagation();
  + break;
  case Key.ARROW_RIGHT: {
  ev.stopPropagation();
  if (this.state.hidden && !this.props.forceExpand) {
  @@ -181,14 +188,11 @@ const RoomSubList = createReactClass({
  },
  onKeyDown: function(ev) {
  - // On ARROW_LEFT collapse the room sublist
  + // On ARROW_LEFT go to the sublist header
  if (ev.key === Key.ARROW_LEFT) {
  ev.stopPropagation();
  - if (!this.state.hidden && !this.props.forceExpand) {
  - this.onClick();
  this._headerButton.current.focus();
  }
  - }
  },
  onRoomTileClick(roomId, ev) {
  