UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3671.0 Safari/537.36

Steps to reproduce the problem:
1. Open test case, scroll vertically with force that can trigger overscroll-behavior chaining up to the viewport/root scroller.
2. Notice chaining isn't contained, though on inspection, the fixed '.scrollport' element has a declaration of `overscroll-behavior: contain`.
3. If you alter the '.scrollport' styles to have a `right:1px` overscroll containment seems to work correctly.

bokan@chromium.org what do ya think? Immediately thought of https://bugs.chromium.org/p/chromium/issues/detail?id=798719

I'm no expert, but recent commits related to overscroll point me to this issue being a possible the cause of regression? https://bugs.chromium.org/p/chromium/issues/detail?id=907601

What is the expected behavior?

What went wrong?
"Overscroll-behavior" when used on a scroller that fits the exact dimenions of the viewport, won't propagate to the implicit root scroller???

Did this work before? Yes Hmmm try a week or so build before Version 73.0.3671.0???

Does this work in other browsers? Yes

Chrome version: 73.0.3671.0  Channel: canary
OS Version: OS X 10.12.6
Flash Version:
 

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