The check sampled getAnimations() once after the sheet showed, which passes or fails on whether WebKit drew a frame in between. It now reads the sheet and backdrop the moment they are inserted, the worst case, and is deterministic: it fails every time against the old classes. The other measurements in the spec already wait on polls, rendered frames or layout.
WebKit in the CI container can go over a second without rendering a frame while events and timers run on; the trace shows the More sheet still sliding in after its animation reported finished. The sheet paints once per frame, so a drag released inside such a stall was never drawn. The spring-back check now holds the finger for two rendered frames, and the settle helper waits for two frames too.
A webkit-iphone project runs one spec: drag, spring back, flick, scroll before drag, a slider sideways, the three closes, focus return, the page's scroll position and pull-to-refresh. CI installs WebKit beside Chromium.
Marc-André Bombeck