Include "beacon" ResourceTiming entry.
The current Resource Timing spec expects beacon resource loads:
> On getting, the initiatorType attribute must return one of the following DOMString values:
> "beacon", if the request is the result of processing the sendBeacon method [Beacon];
1. Load https://tests.caniuse.com/?feat=beacon
2. Wait a while so beacons could be fulfilled
3. js> performance.getEntriesByType("resource")
=> No "beacon" entries
- No other browser I tested included beacon loads in Resource Timing
- Note adding entries to the performance timeline exposes when the beacon was sent / response received. I don't think thats a bad thing.