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

Suspecting Commit#
https://pdfium.googlesource.com/pdfium.git/+/7726a581626bbb72d6ab294ae1adbad4ca10dfb0

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

This is an out of memory condition.

ClusterFuzz has detected this issue as fixed in range 498648:498677.

Detailed report: https://clusterfuzz.com/testcase?key=6378655776505856

Fuzzer: marty_html_twiddler
Job Type: windows_asan_chrome_no_sandbox
Platform Id: windows

Crash Type: Null-dereference WRITE
Crash Address: 0x00000000
Crash State:
  base::win::ForceCrashOnSigAbort
  raise
  FX_OutOfMemoryTerminate
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=windows_asan_chrome_no_sandbox&range=495902:496126
Fixed: https://clusterfuzz.com/revisions?job=windows_asan_chrome_no_sandbox&range=498648:498677

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6378655776505856

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.