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

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/f791eeeca58c648ee7b55e439e0368129a7db990

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

The suspected change is not within the regression range. Can we get a bisect?

Assigning to concern owner from Predator results --
[ES6 modules] Document ModuleScript TraceWrapper paths by kouhei@chromium.org
Changed files ModuleScript.h, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files ModuleScript.h, with the same CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

Reland "Textarea resize-able only to larger; min-height and min-width properly set" by tkent@chromium.org
Changed files Element.cpp, Element.h, ElementRareData.cpp, ElementRareData.h, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files Element.cpp, Element.h, ElementRareData.cpp, ElementRareData.h, with the same CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

TraceWrapper Modulator from LocalDOMWindow/WorkletGlobalScope by kouhei@chromium.org
Changed files LocalDOMWindow.cpp, LocalDOMWindow.h, with the same CrashedDirectory(third_party/WebKit/Source/core/frame) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2) Changed files Modulator.cpp, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files LocalDOMWindow.cpp, LocalDOMWindow.h, with the same CrashedComponent(Blink>Internals) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2) Changed files Modulator.cpp, with the same 
CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

[ES6 modules] Update module script error state predicate and transition. by kouhei@chromium.org
Changed files ModulatorImpl.cpp, ModuleMapTest.cpp, ModulePendingScript.cpp, ModuleScript.cpp, ModuleScript.h, ScriptModuleResolver.h, ScriptModuleResolverImpl.cpp, ScriptModuleResolverImpl.h, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files ModulatorImpl.cpp, ModuleMapTest.cpp, ModulePendingScript.cpp, ModuleScript.cpp, ModuleScript.h, ScriptModuleResolver.h, ScriptModuleResolverImpl.cpp, ScriptModuleResolverImpl.h, with the same CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

Consider service worker CORS check when checking subresource integrity by hintzed@google.com
Changed files SubresourceIntegrityTest.cpp, with the same CrashedDirectory(third_party/WebKit/Source/core/frame) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2)
Changed files SubresourceIntegrityTest.cpp, with the same CrashedComponent(Blink>Internals) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2)

[ES6 modules] TraceWrapper from ScriptLoader and ModuleTreeLinkerRegistry by kouhei@chromium.org
Changed files script-module-inline-error-gc-expected.txt, script-module-inline-error-gc.html, MockScriptElementBase.h, Modulator.h, ModulatorImpl.cpp, ModulatorImpl.h, ModuleMapTest.cpp, ModulePendingScript.cpp, ModulePendingScript.h, ModuleScript.cpp, ModuleScript.h, PendingScript.h, ScriptElementBase.cpp, ScriptElementBase.h, ScriptLoader.cpp, ScriptLoader.h, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files MockScriptElementBase.h, Modulator.h, ModulatorImpl.cpp, ModulatorImpl.h, ModuleMapTest.cpp, ModulePendingScript.cpp, ModulePendingScript.h, ModuleScript.cpp, ModuleScript.h, PendingScript.h, ScriptElementBase.cpp, ScriptElementBase.h, ScriptLoader.cpp, ScriptLoader.h, with the same CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

Add factory creation methods for creating local and remote main frames. by dcheng@chromium.org
Changed files FrameTestHelpers.cpp, with the same CrashedDirectory(third_party/WebKit/Source/core/frame) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2)
Changed files FrameTestHelpers.cpp, with the same CrashedComponent(Blink>Internals) as Frame.h (in frame#1), LocalFrame.cpp (in frame#2)

Removed calls to RefPtr::Release in return statements with auto move. by bugsnash@chromium.org
Changed files Element.cpp, with the same CrashedDirectory(third_party/WebKit/Source/core/dom) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)
Changed files Element.cpp, with the same CrashedComponent(Blink>DOM) as Document.cpp (in frame#3, frame#4, frame#5, frame#6)

Suspecting Commit#
https://chromium.googlesource.com/chromium/src/+/78634df3327f642c0334519ff4f1bf290712146b

@kouhei -- Could you please look into the issue, kindly re-assign if it has nothing to do with your changes.
Thank You.

DOM team currently doesn't own core/frame nor DOMWindow.

Automatically applying components based on information from OWNERS files. If this seems incorrect, please apply the Test-Predator-Wrong-Components label.

ClusterFuzz has detected this issue as fixed in range 509075:509091.

Detailed report: https://clusterfuzz.com/testcase?key=5198547220955136

Fuzzer: inferno_layout_test_unmodified
Job Type: linux_asan_content_shell_drt
Platform Id: linux

Crash Type: Null-dereference READ
Crash Address: 0x000000000048
Crash State:
  blink::LocalFrame::Client
  blink::Document::open
  blink::Document::open
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=linux_asan_content_shell_drt&range=482161:482264
Fixed: https://clusterfuzz.com/revisions?job=linux_asan_content_shell_drt&range=509075:509091

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5198547220955136

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 5198547220955136 is verified as fixed, so closing issue as verified.

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