src/vs/workbench/services/timer/browser/timerService.ts/PerfMarks/getDuration
class PerfMarks:	getDuration(from: string, to: string): number {
		const fromEntry = this._findEntry(from);
		if (!fromEntry) {
			return 0;
		}
		const toEntry = this._findEntry(to);
		if (!toEntry) {
			return 0;
		}
		return toEntry.startTime - fromEntry.startTime;
	}