An extremely rough input latency web perf polyfill, exploring the possibilities.
The associated rough proposal for an Event Timing web performance API can be found here.
This is not intended for production use, just to explore the API space.
The demo here contains a box with a slow click handler, a button to fetch resources, and a button to download a trace, containing the information recorded by a PerformanceObserver.
Here's a sample trace.
