src/vs/base/browser/ui/menu/menubar.ts/MenuBar/getWidth
class MenuBar:	getWidth(): number {
		if (this.menuCache) {
			const left = this.menuCache[0].buttonElement.getBoundingClientRect().left;
			const right = this.hasOverflow ? this.overflowMenu.buttonElement.getBoundingClientRect().right : this.menuCache[this.menuCache.length - 1].buttonElement.getBoundingClientRect().right;
			return right - left;
		}

		return 0;
	}