src/vs/workbench/contrib/notebook/common/notebookPerformance.ts/NotebookPerfMarks/mark
class NotebookPerfMarks:	mark(name: PerfName): void {
		if (this._marks[name]) {
			console.error(`Skipping overwrite of notebook perf value: ${name}`);
			return;
		}

		this._marks[name] = Date.now();
	}