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

		return 0;
	}