Predator and CL did not provide any possible suspects.
Using Code Search for the file, "SelectorChecker.cpp" assigning to the concern owner.
Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/0e2caa4b6dc7715e9d08e77f46e1dcdf28825405

@rune -- 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 470772:470990.

Detailed report: https://clusterfuzz.com/testcase?key=6611402908499968

Fuzzer: inferno_twister
Job Type: linux_ubsan_chrome
Platform Id: linux

Crash Type: Integer-overflow
Crash Address: 
Crash State:
  blink::CSSSelector::RareData::MatchNth
  blink::SelectorChecker::CheckPseudoClass
  blink::SelectorChecker::MatchSelector
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_ubsan_chrome&range=370022:370027
Fixed: https://clusterfuzz.com/revisions?job=linux_ubsan_chrome&range=470772:470990

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6611402908499968


See https://dev.chromium.org/Home/chromium-security/bugs/reproducing-clusterfuzz-bugs for more information.

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