Predator and CL did not provide any possible suspects.
Using Code Search for the file, "blink_test_controller.cc" assigning to the concern owner.

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/d565a833804f202c057a33337e63d55793144cec

@lukasza -- 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 495550:495592.

Detailed report: https://clusterfuzz.com/testcase?key=4785484063834112

Fuzzer: mbarbella_js_mutation_layout
Job Type: windows_syzyasan_content_shell
Platform Id: windows

Crash Type: Null-dereference
Crash Address: 0x00000003
Crash State:
  content::BlinkTestController::OnDumpFrameLayoutResponse
  base::internal::Invoker<base::internal::BindState<void
  base::Callback<void __cdecl
  
Memory Tool: SYZYASAN

Regressed: https://clusterfuzz.com/revisions?job=windows_syzyasan_content_shell&range=483918:483919
Fixed: https://clusterfuzz.com/revisions?job=windows_syzyasan_content_shell&range=495550:495592

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4785484063834112

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 4785484063834112 is verified as fixed, so closing issue as verified.

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