This PR adjusts our scrolling implementation to delay the generation of
ScrollWheel events until we receive a complete frame.
Note that our implementation is still a bit off-spec, as we don't delay
any other kind of events. But it's been working so far on a variety of
compositors and the other events contain complete data; so I'll hold off
on that refactor for now.
Release Notes:
- N/A
Mikayla Maki
3289188e0a