Run the benchmark on a variety of devices you will see it behave differently sometimes it hits the scroll extent sometimes it doesn't. Specifically on a Nexus 5 it does and a Nexus 5X it doesn't.

I believe the test needs some refinement because before change

https://crrev.com/5494d50ab65532c64a28e91e23b0a722ebbfe8ed

On a Nexus 5X the page scrolled to the scroll extent and caused the overscroll glow. After the change it doesn't which it then it infinitely scrolls more content. I believe the desired behavior after the change was the originally intended effect.

The change in question caused performance regression: https://bugs.chromium.org/p/chromium/issues/detail?id=679324

which was then closed out because the desired behavior is actually correct. The infinite content caused the page to have more nodes and consume more memory.