Chrome Version: 73.0.3674.0
OS: ChromeOS

What steps will reproduce the problem?
(1)Navigate to any scrollable site
(2)scroll/fling in up and down directions a few times.

What is the expected result?
We should receive ET_SCROLL_FLING_CANCEL events each time the user puts their fingers on touchpad, and ET_SCROLL_FLING_START each time the user lifts their fingers. The correct event sequence should be:
(ET_SCROLL_FLING_CANCEL, (ET_SCROLL)xN, ET_SCROLL_FLING_START)xM
i.e. between an ET_SCROLL event and its previous ET_SCROLL_FLING_START, we should receive a ET_SCROLL_FLING_CANCEL event.

What happens instead?
Sometimes no ET_SCROLL_FLING_CANCEL arrives when the user puts their fingers on touchpad and ET_SCROLL arrives right after ET_SCROLL_FLING_START.

I added logs to https://cs.chromium.org/chromium/src/ui/events/event_dispatcher.cc?gsn=ack_result&g=0&l=193 to check the arriving events.