function ResizeObserver(callback) {
            if (!(this instanceof ResizeObserver)) {
                throw new TypeError('Cannot call a class as a function.');
            }
            if (!arguments.length) {
                throw new TypeError('1 argument required, but only 0 present.');
            }
            var controller = ResizeObserverController.getInstance();
            var observer = new ResizeObserverSPI(callback, controller, this);
            observers.set(this, observer);
        }
Creates a new instance of ResizeObserver.

@param {ResizeObserverCallback} callback - Callback that is invoked when
     dimensions of the observed elements change.