Find it and CL did not provide any possible suspects.
Using Code Search for the file, "WebPrivatePtr.h" assigning to the concern owner --

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/db91ee76e2ad96a39936bf687a19a93ed547653a

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

ClusterFuzz has detected this issue as fixed in range 43366:43373.

Detailed report: https://cluster-fuzz.appspot.com/testcase?key=5841110149890048

Fuzzer: mbarbella_js_mutation_layout
Job Type: linux_asan_chrome_v8
Platform Id: linux

Crash Type: UNKNOWN READ
Crash Address: 0x000000000270
Crash State:
  blink::WebString::WebString
  blink::WebURL::WebURL
  blink::WebDocument::url
  
Sanitizer: address (ASAN)

Regressed: V8: 37442:37458
Fixed: V8: 43366:43373

Reproducer Testcase: https://cluster-fuzz.appspot.com/download/AMIfv971nHhXSAYznw0fGBuCQvUxjyIauc_K71nyaUmD4zw61fHSQHL1B3rYB7gbfRj16uZUQKXQUbuWR2vp3qsfpxdUWw5OEoxmAM3UkhXl9Ty8NdJsH327MNmTz-fw7WMVdpju1lonw2h_uvHHbib6nRhw1AFB-0sxhKHt4sQaSakHNgFetmOrNvXVmHnl9CO7QHmc5Rf8lsUUKkl4eINrdn_wT_9WWQeVgYlKT_64m-fIyF6OXXbovY3Koxg9bLNAN6KKLLLM313pCzcoD1lN1zSHmPy6kQd_SxMuWy3m0UbUHajGJxjYBRQT_6KtAUnNl2Vi33wrQdk46AKTB2uwetbOWUYjUTrRkHbN_0QcR8voIrfg_l8?testcase_id=5841110149890048


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.

ClusterFuzz testcase 5841110149890048 is verified as fixed, so closing issue.

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