The Paint Timing Markers feature allows you to view colour-coded markings in the Performance Panel. These Timings include:
You can correlate these markings with the rendering data shown in a Performance Panel profile to understand which resources contributed to certain events.
I've written an article about this subject in: Improving Performance with the Paint Timing API.
Note: This is a hidden experiment in DevTools. In Canary DevTools, go to Settings > Experiments > Press shift 6 times > Enable the Paint Timing Markers experiment.