src/vs/editor/browser/config/elementSizeObserver.ts/ElementSizeObserver/startObserving
class ElementSizeObserver:	public startObserving(): void {
		if (!this._resizeObserver && this._referenceDomElement) {
			this._resizeObserver = new ResizeObserver((entries) => {
				if (entries && entries[0] && entries[0].contentRect) {
					this.observe({ width: entries[0].contentRect.width, height: entries[0].contentRect.height });
				} else {
					this.observe();
				}
			});
			this._resizeObserver.observe(this._referenceDomElement);
		}
	}