Predator did not provide any possible suspects.
Assigning to concern owner from CL --
https://chromium.googlesource.com/chromium/src/+log/aca9ff5295e91d1bba92e50285bf1ee2893de5e4..4f4d0e4f9122db7ee36d5bbd3b086d998aa9e9c1?pretty=fuller

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/c5614bacedb1f26619aac05832a21c51143ba2d6

@keishi -- 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 500471:500496.

Detailed report: https://clusterfuzz.com/testcase?key=5738806027485184

Fuzzer: ifratric-browserfuzzer-v3
Job Type: linux_ubsan_chrome
Platform Id: linux

Crash Type: CHECK failure
Crash Address: 
Crash State:
  count <= MaxElementCountInBackingStore<T>() in HeapAllocator.h
  blink::HeapAllocator::QuantizedSize<>
  blink::UndoStep::Append
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_ubsan_chrome&range=464875:464913
Fixed: https://clusterfuzz.com/revisions?job=linux_ubsan_chrome&range=500471:500496

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5738806027485184

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 5738806027485184 is verified as fixed, so closing issue as verified.

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