Inject this javascript to your webview and it reports scroll state of the webview, including start, end and fling.
http://ladjzero.me/example/fling.js
Or scan the QR code
It calls window.onScrollStateChange once scroll state changes.
Possible states are start, fling, end.
Works on chrome based webview which can fire touchend event after touchmove.
For other webviews I have to listen to scroll event instead.