I think this is a bug, because from TouchEvent the pressure (a unique feature of stylus) cannot be taken.

Confirmed this is a regression.
The issue didn't reproduce in 55.0.2883.34. Chrome OS 8872.34.0 kevin.

This breaks Stylus app on demo mode, which runs on Chromebooks on retail stores. https://bugs.chromium.org/p/chromium/issues/detail?id=699413
There is little hope to workaround this because unlike pointerevent, touchevent doesn't have pressure, needed by the app.

Will it be possible to cherry-pick a fix to M57?

I believe you need a touch-action: none set on the canvas. Have you tried that in your demo app?

ie; try this: http://output.jsbin.com/fitasewaqo

Code should be listening to either pointer events or touch events OR should be calling preventDefault on the pointerdown event to prevent touch events from being fired at all.  

But why would this have behaved that way in M55?  Should we request a bisect?

oka@: The repro you sent has a few issues as dtapuska@ and rbyers@ mentioned above, the missing "touch-action:none" is the main one. But this shouldn't change after M55.

Could you please confirm if both:
  (a) the demo app you mentioned and
  (b) your repro above
show the regression?

Thank you for the explanation. I will add touch-action to demo app to fix the issue in demo app.

Seems we don't need any change in chromium, so closing the bug. Feel free to reopen if this is not the case.