sahel@ this sounds like we are getting the GestureFlingStart but aren't receiving a GestureFlingCancel for this hardware. Perhaps you can give it a try and figure out the event stream.

Version 54.0.2840.68 beta (64-bit)
Platform 8743.69.0 (Official Build) beta-channel panther
Firmware Google_Panther.4920.24.26

It looks like putting 2 fingers down will stop the scrolling now, but if I move my fingers without halting scrolling first, my scroll gesture fights against the inertia of the previous fling, as before.

This is also easily replicated with a touchpad and an external mouse. Do a touchpad fling on a long document, then try to use the mouse wheel. The mouse doesn't cancel out the existing fling.

Hmm, the problem only happens on certain pages. It does not happen on simple web pages or text files. But it does happen in the PDF reader and (I think) some pages where not every element scrolls (like bugs.chromium.org).

So not all scrolling codepaths have this problem.

I couldn't reproduce the bug using Logitech T650, on my Chromebook:
Version 57.0.2925.0 (64-bit)
Platform 8510.0.0 (Official Build) dev-channel samus test
Firmware Google_Samus.6300.174.0

However, I could reproduce it on 56.0.2906.0 (64-bit) and 57.0.2925.0 (64-bit) chromium builds on Linux and Windows, using the same Logitech T650 touchpad. This seems like a regression, because I couldn't reproduce the bug on 54.0.2840.100/99 (64-bit) on neither of the platforms.

I will take another look

The NextAction date has arrived: 2017-11-30