Browser scroll performance optimization can delay OnDemandList rendering

[msssk]

dgrid's OnDemandList uses debouncing or throttling to optimize rendering performance during scrolling. The debounce and throttle implementations are dependent on setTimeout, which has been targeted by browser vendors for "optimization", which means the callback passed to setTimeout may be executed long after the specified delay.

This has been observed impacting moderately complicated grids in Chrome on MacOS. The result is that when you perform a large rapid scroll, when you stop scrolling there is a significant delay (2-10 seconds) before the setTimeout callback is executed, data is fetched and rows are rendered.