src/vs/css.ts/linkTagExists
function linkTagExists(name: string, cssUrl: string): boolean {
	const links = document.getElementsByTagName('link');
	for (let i = 0, len = links.length; i < len; i++) {
		const nameAttr = links[i].getAttribute('data-name');
		const hrefAttr = links[i].getAttribute('href');
		if (nameAttr === name || hrefAttr === cssUrl) {
			return true;
		}
	}
	return false;
}