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

Suspecting Commit#
https://skia.googlesource.com/skia.git/+/2de8cfadc34cd92a6f99659fa565c137b386fa5f

@robertphillips -- 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 491107:491189.

Detailed report: https://clusterfuzz.com/testcase?key=6523252947288064

Fuzzer: libFuzzer_paint_op_buffer_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Integer-overflow
Crash Address: 
Crash State:
  SkIRect::inset
  GrRenderTargetContext::setupDstProxy
  GrRenderTargetContext::addDrawOp
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=490727:490745
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=491107:491189

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=6523252947288064


See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md 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 6523252947288064 is verified as fixed, so closing issue as verified.

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