function getNeededRows( selector, containerSelector = defaultContainerSelector ) {
	const minHeights = getCachedMinHeights();
	const minHeight = minHeights.get( selector );
	if ( !minHeight ) {
		throw new Error( `Can't calculate needed rows, invalid selector: ${selector}` );
	}

	// the route's view hasn't been inserted yet: choose the parent element
	const container = document.querySelector( containerSelector ) || document.body;

	return 1 + ceil( container.clientHeight / minHeight );
}
@param {string} selector
@param {string?} containerSelector
@return {number}