We don't do snapping now, but a wpt sends wheel events with SCROLLDELTA_PIXEL, thus the wpt doesn't work expected.

Are there cases where we get wheel events with SCROLLDELTA_PIXEL in production?

I believe the original reason we didn't snap here was that, before we had PanGestureInput, trackpads would generate wheel events with pixel deltas, and we didn't want to snap after each event, only when the fingers are lifted (which at the time was handled when the main thread received an eWheelOperationEnd).

Oops. Then doing simply snapping in the cases of SCROLLDELTA_PIXEL isn't a good idea. I don't know whether there's any devices sending wheel events with SCROLLDELTA_PIXEL in production.

I suppose why web drivers uses such pixel-based API is the scroll destination is predictable? CCing :jgraham.

I'm going to mark this as P2 for addressing the WPT issue in some way (but the way may be different than the current bug title, "doing scroll snap for wheel events with SCROLLDELTA_PIXEL").