[PerformanceTimeline] Returning Navigation Timing attributes in High Resolution Time

In order for Navigation Timing to take its respective place in the timeline, Section 4.4 of Performance Timeline defines a PerformanceEntry object for Navigation Timing that contains the "name", "entryType", "startTime" and "duration" attributes. With "startTime" and "duration", when looking at the entire timeline, the page navigation time is included along with resource and developer script data.

We previously had not considered adding the Navigation Timing attributes to the PerformanceEntry for Navigation Timing, as these attributes already exist in PerformanceTiming, as defined in the Navigation Timing spec.

However, whereas Resource Timing and User Timing benefit from having sub-millisecond timing information due to High Resolution Time (DOMHighResTimeStamp), individual Navigation Timing attributes are only given in millisecond resolution on the PerformanceTiming interface. Further, the attributes are in a different timebase, so it's difficult to compare the fetchStart of the navigation with the fetchStart of a particular resource, as an example.

For compatibility reasons, we do not want to change PerformanceTiming. However, should we consider adding the Navigation Timing attributes to the navigation PerformanceEntry? Each attribute would return a DOMHighResTimeStamp with the attribute definition linked to the Navigation Timing spec definition.

E.g., when invoking getEntries("navigation"), you would get the following object:

interface PerformanceNavigationTiming : PerformanceEntry {
  //Defined in PerformanceEntry
  // readonly DOMString name;
  // readonly DOMString entryType;
  // readonly DOMHighResTimeStamp startTime;
  // readonly DOMHighResTimeStamp duration;


  readonly attribute DOMHighResTimeStamp  navigationStart;
  readonly attribute DOMHighResTimeStamp  unloadEventStart;
  readonly attribute DOMHighResTimeStamp  unloadEventEnd;
  readonly attribute DOMHighResTimeStamp  redirectStart;
  readonly attribute DOMHighResTimeStamp  redirectEnd;
  readonly attribute DOMHighResTimeStamp  fetchStart;
  readonly attribute DOMHighResTimeStamp  domainLookupStart;
  readonly attribute DOMHighResTimeStamp  domainLookupEnd;
  readonly attribute DOMHighResTimeStamp  connectStart;
  readonly attribute DOMHighResTimeStamp  connectEnd;
  readonly attribute DOMHighResTimeStamp  secureConnectionStart;
  readonly attribute DOMHighResTimeStamp  requestStart;
  readonly attribute DOMHighResTimeStamp  responseStart;
  readonly attribute DOMHighResTimeStamp  responseEnd;
  readonly attribute DOMHighResTimeStamp  domLoading;
  readonly attribute DOMHighResTimeStamp  domInteractive;
  readonly attribute DOMHighResTimeStamp  domContentLoadedEventStart;
  readonly attribute DOMHighResTimeStamp  domContentLoadedEventEnd;
  readonly attribute DOMHighResTimeStamp  domComplete;
  readonly attribute DOMHighResTimeStamp  loadEventStart;
  readonly attribute DOMHighResTimeStamp loadEventEnd;
};

Let's discuss in the call today.

Thanks,
Jatinder