Gesture Scroll DOM events, namely “gesturescrollstart”, “gesturescrollupdate” and “gesturescrollend” are non-standard APIs, which were added to Blink for use in plugins, but it appears they were also exposed to the web unintentionally. Plugins are no longer web-exposed since the deprecation of Google Native Client (NaCl). WebKit Bug: https://bugs.webkit.org/show_bug.cgi?id=92281 Changelog: https://bugs.webkit.org/attachment.cgi?id=155046&action=prettypatch
Currently, this API doesn’t work in all situations. It only works when there is a non-composited scroller. These events are related to compositing state, and compositing state is not meant to have observable behavior impact and in Blink will vary depending on display type and other factors.