paint_timing library Null safety

Paint Timing 1

https://w3c.github.io/paint-timing/

Classes

PerformancePaintTiming
The interface of the Paint Timing API provides timing information about "paint" (also called "render") operations during web page construction. "Paint" refers to conversion of the render tree to on-screen pixels. An application can register a PerformanceObserver for "paint" performance entry types and the observer can retrieve the times that paint events occur. Use this information to help identify areas that take too long to provide a good user experience.