function ListSelectionController(selectionModel) {
    this.selectionModel_ = selectionModel;
  }
Creates a selection controller that is to be used with lists. This is
implemented for vertical lists but changing the behavior for horizontal
lists or icon views is a matter of overriding {@code getIndexBefore},
{@code getIndexAfter}, {@code getIndexAbove} as well as
{@code getIndexBelow}.

@param {cr.ui.ListSelectionModel} selectionModel The selection model to
    interact with.

@constructor
@extends {!cr.EventTarget}