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/+/6ce9d62f9ff5113c4a5c2f39ebf998187feedc5c

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

ClusterFuzz has detected this issue as fixed in range 495551:495853.

Detailed report: https://clusterfuzz.com/testcase?key=6176690241011712

Fuzzer: marty_html_twiddler
Job Type: windows_asan_chrome
Platform Id: windows

Crash Type: Null-dereference READ
Crash Address: 0x00000008
Crash State:
  blink::ScrollableArea::GetScrollAnimator
  blink::Scrollbar::ScrollableAreaTargetPos
  blink::Scrollbar::ThumbWillBeUnderMouse
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=windows_asan_chrome&range=494105:494256
Fixed: https://clusterfuzz.com/revisions?job=windows_asan_chrome&range=495551:495853

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6176690241011712

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 6176690241011712 is verified as fixed, so closing issue as verified.

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