function TreeOutline(nonFocusable)
{
    this._createRootElement();

    this.selectedTreeElement = null;
    this.expandTreeElementsWhenArrowing = false;
    /** @type {?function(!TreeElement, !TreeElement):number} */
    this._comparator = null;

    this._contentElement = this._rootElement._childrenListNode;
    this._contentElement.addEventListener("keydown", this._treeKeyDown.bind(this), true);

    this.setFocusable(!nonFocusable);

    this.element = this._contentElement;
}
@constructor
@extends {WebInspector.Object}
@param {boolean=} nonFocusable