Scrolling in Windows noticeably slower than other browsers

[jonathandturner]

For the same hardware/setup, I'm seeing scrolling in Windows being noticeably slower than other browsers. I made sure I was running in release mode, and still see the behaviour.

Eyeballing it, it seems that we're seeing:

• Slow detection that a scrolling event is occuring. Other browsers seem to switch to scrolling quicker than Servo.
• Sputtering scrolling. The scroll isn't smooth and continuous like Chrome or Edge, but instead stops and starts.
• Scrolling momentum feels low. Compared to other browsers, you would expect better momentum after you release the scroll, so the scrolling feels more buttery and natural. In Servo, the scroll stops almost immediately, and doesn't have a comfortable momentum.
• Scrolling itself feels much slower than other browsers. This may be Windows-specific, because I see a much faster scroll for similar hardware in macOS.