src/vs/workbench/contrib/notebook/common/notebookPerformance.ts/mark
export function mark(resource: URI, name: PerfName): void {
	const key = resource.toString();
	if (!perfMarks.has(key)) {
		let perfMark: PerformanceMark = {};
		perfMark[name] = Date.now();
		perfMarks.set(key, perfMark);
	} else {
		if (perfMarks.get(key)![name]) {
			console.error(`Skipping overwrite of notebook perf value: ${name}`);
			return;
		}
		perfMarks.get(key)![name] = Date.now();
	}
}