Predator and CL could not provide any possible suspects.
Using Code Search for the file, "scrollablearea.cpp" assigning to the concern owner.

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/489ca56b55f5f1d791732d2729141a1217f239d2

@pdr -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

I think this may be:
Reland "Overlay Scrollbar track not block hit test"
https://chromium.googlesource.com/chromium/src/+/2a88dac7dd3caf5155d4e82f08c86d12484dbf18

Note that this is in the second page of the regression range (have to click next at the bottom of the regression range page).

Yes, this CL (crrev.com/c/616901) also fix this 

ClusterFuzz has detected this issue as fixed in range 495531:495550.

Detailed report: https://clusterfuzz.com/testcase?key=4954864923967488

Fuzzer: inferno_twister
Job Type: windows_syzyasan_chrome
Platform Id: windows

Crash Type: Null-dereference
Crash Address: 0x0000000b
Crash State:
  blink::ScrollableArea::GetScrollAnimator
  blink::Scrollbar::ThumbWillBeUnderMouse
  base::ObserverListBase<ui::PlatformEventObserver>::begin
  
Memory Tool: SYZYASAN

Regressed: https://clusterfuzz.com/revisions?job=windows_syzyasan_chrome&range=494105:494239
Fixed: https://clusterfuzz.com/revisions?job=windows_syzyasan_chrome&range=495531:495550

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4954864923967488

Additional requirements: Requires Gestures

See https://github.com/google/clusterfuzz-tools for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 4954864923967488 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.