PerformanceMeasure
PerformanceMeasure is an abstract interface for PerformanceEntry objects with an entryType of "measure". Entries of this type are created by calling performance.measure() to add a named DOMHighResTimeStamp (the measure) between two marks to the browser's performance timeline.
var PerformanceMeasure: {
prototype: PerformanceMeasure;
new (): PerformanceMeasure;
};