When TouchpadFling gestures are generated the wheel event generation occurs inside the renderer. This causes a performance draw back if there are wheel event listeners in javascript as the entire fling is moved to the main thread causing main thread scrolling.

See:
https://cs.chromium.org/chromium/src/ui/events/blink/input_handler_proxy.cc?q=input_handler_proxy.cc&sq=package:chromium&l=1246

It should be possible that events are sent to the main thread and executed by the fling is then processed on the compositor thread.

Perhaps the event generation (from the fling gesture) should be done in the browser process to make it similar to how this happens on Mac.