Function getPositionObserver

ads/inabox/position-observer.js:181–185

(win)

 * @return {!PositionObserver}
 */
export function getPositionObserver(win) {
  win[AMP_INABOX_POSITION_OBSERVER] =
    win[AMP_INABOX_POSITION_OBSERVER] || new PositionObserver(win);
  return win[AMP_INABOX_POSITION_OBSERVER];
}