function _updateListItemSelection(listItem, selectedDoc) {
        var shouldBeSelected = (selectedDoc && $(listItem).data(_FILE_KEY).fullPath === selectedDoc.file.fullPath);
        
        // cast to Boolean needed because toggleClass() distinguishes true/false from truthy/falsy
        $(listItem).toggleClass("selected", Boolean(shouldBeSelected));
    }
Updates the appearance of the list element based on the parameters provided.
@private
@param {!HTMLLIElement} listElement
@param {?Document} selectedDoc