https://chromium-swarm.appspot.com/task?id=38c441b6b03d4510&refresh=10&show_raw=1

[00450.655] 03530.03557> 1 test crashed:
[00450.655] 03530.03557>     BrowserThreadTest.PostTask (../../content/browser/browser_thread_unittest.cc:121)

...
[00055.782] 03530.03557> [327/4670] BluetoothBlocklistTest.RemoveExcludedUuids_Matching (0 ms)
[00055.782] 03530.03557> [328/4670] BluetoothBlocklistTest.VerifyDefaultBlocklistSize (0 ms)
[00055.783] 03530.03557> [329/4670] BluetoothBlocklistTest.VerifyDefaultExcludeList (1 ms)
[00055.783] 03530.03557> [330/4670] BluetoothBlocklistTest.VerifyDefaultExcludeReadList (0 ms)
[00057.346] 03530.03774> [3:766536313:0922/211519.410228:57346211:ERROR:sequenced_worker_pool.cc(1373)] shutdown_called_=0
[00057.362] 01119.01152> <== fatal exception: process content_unittests[26319] thread pthread_t:0x4d05ee5d4b30[27546]
[00057.362] 01119.01152> <== fatal page fault, PC at 0x562c988bff9a
[00057.364] 01119.01152>  CS:                   0 RIP:     0x562c988bff9a EFL:            0x10202 CR2:               0x18
[00057.364] 01119.01152>  RAX:                  0 RBX:     0x4d05ee5d4b50 RCX:     0x47ebdee870e0 RDX:                0x1
[00057.364] 01119.01152>  RSI:                0x1 RDI:                  0 RBP:                0x1 RSP:     0x52f16438d4d0
[00057.365] 01119.01152>   R8:     0x47570b5cf7c4  R9:     0x52f16438d440 R10:               0x20 R11:              0x202
[00057.365] 01119.01152>  R12:                  0 R13:               0x18 R14:                  0 R15:                  0
[00057.365] 01119.01152>  errc:               0x6
[00057.365] 01119.01152> bottom of user stack:
[00057.366] 01119.01152> 0x000052f16438d4d0: ee5d4b30 00004d05 6951bca0 00000000 |0K]..M....Qi....|
[00057.366] 01119.01152> 0x000052f16438d4e0: 6951bca0 00000000 0b5cf7b8 00004757 |..Qi......\.WG..|
[00057.366] 01119.01152> 0x000052f16438d4f0: 6438d7c0 000052f1 ee5d4b50 00004d05 |..8d.R..PK]..M..|
[00057.366] 01119.01152> 0x000052f16438d500: 6438d680 000052f1 00000000 00000000 |..8d.R..........|
[00057.367] 01119.01152> 0x000052f16438d510: 00000000 00000000 988bfade 0000562c |............,V..|
[00057.367] 01119.01152> 0x000052f16438d520: 6438d640 000052f1 62b4b38b 00005010 |@.8d.R.....b.P..|
[00057.367] 01119.01152> 0x000052f16438d530: 0b5cf7a0 00004757 dee8b000 000047eb |..\.WG.......G..|
[00057.368] 01119.01152> 0x000052f16438d540: dee870e0 000047eb 00000000 00000000 |.p...G..........|
[00057.368] 01119.01152> 0x000052f16438d550: 0b5cf7b8 00004757 0b5cf7b8 00004757 |..\.WG....\.WG..|
[00057.368] 01119.01152> 0x000052f16438d560: 6951bca0 00005010 629f2417 00005010 |..Qi.P...$.b.P..|
[00057.368] 01119.01152> 0x000052f16438d570: 6438d558 000052f1 dee870e0 000047eb |X.8d.R...p...G..|
[00057.369] 01119.01152> 0x000052f16438d580: dee870e0 000047eb dee870f0 000047eb |.p...G...p...G..|
[00057.369] 01119.01152> 0x000052f16438d590: 00000001 00000000 dee870e0 000047eb |.........p...G..|
[00057.369] 01119.01152> 0x000052f16438d5a0: 6438d568 000052f1 dee870e0 000047eb |h.8d.R...p...G..|
[00057.369] 01119.01152> 0x000052f16438d5b0: dee870f0 000047eb dee8b000 000047eb |.p...G.......G..|
[00057.370] 01119.01152> 0x000052f16438d5c0: 6438d568 000052f1 62b69f30 00005010 |h.8d.R..0..b.P..|
[00057.370] 01119.01152> arch: x86_64
[00057.371] 01119.01152> dso: id=6059863b129a49d829760aa4be72cc3742a085c6 base=0x74aea2ff4000 name=<vDSO>
[00057.371] 01119.01152> dso: id=f235c1e16717d9197e499a200425e0681468b830 base=0x649773708000 name=libfdio.so
[00057.372] 01119.01152> dso: id=5ddf965ecef4f7eaba5aa9b7b240503f27a2595a base=0x562c988a7000 name=libc.so
[00057.372] 01119.01152> dso: id=b1bbdfea7b0c546e base=0x5010573bb000 name=app:content_unittests
[00057.372] 01119.01152> dso: id=4e555334ce701b327433bb28771402652496af06 base=0x1984d3414000 name=liblaunchpad.so
[00057.397] 03530.03557> [331/4670] BrowserURLHandlerImplTest.BasicRewriteAndReverse (42 ms)
[00057.397] 03530.03557> [332/4670] BrowserURLHandlerImplTest.NullHandlerReverse (41 ms)
[00057.398] 03530.03557> [333/4670] BrowserURLHandlerImplTest.ViewSourceReverse (42 ms)
[00057.398] 03530.03557> [334/4670] BrowsingDataFilterBuilderImplTest.Noop (1 ms)
[00057.398] 03530.03557> [335/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainGURLWhitelist (2 ms)
[00057.399] 03530.03557> [336/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainGURLBlacklist (1 ms)
[00057.400] 03530.03557> [337/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainMatchesCookiesWhitelist (9 ms)
[00057.400] 03530.03557> [338/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainMatchesCookiesBlacklist (10 ms)
[00057.401] 03530.03557> [339/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainMatchesChannelIDsWhitelist (1 ms)
[00057.401] 03530.03557> [340/4670] BrowsingDataFilterBuilderImplTest.RegistrableDomainMatchesChannelIDsBlacklist (0 ms)
#01: pc 0x562c988bff9a sp 0x52f16438d4d0 (libc.so,0x18f9a)
#02: pc 0x562c988bfade sp 0x52f16438d520 (libc.so,0x18ade)
#03: base::ConditionVariable::Signal() at ../../../../work/cr/src/base/synchronization/condition_variable_posix.cc:138
#04: DecrementNumPendingUndelayedTasks at ../../../../work/cr/src/base/task_scheduler/task_tracker.cc:530
#05: RunNextTask at ../../../../work/cr/src/base/task_scheduler/task_tracker.cc:258
#06: ThreadMain at ../../../../work/cr/src/base/task_scheduler/scheduler_worker.cc:72
#07: ThreadFunc at ../../../../work/cr/src/base/threading/platform_thread_posix.cc:77
#08: pc 0x562c988c0526 sp 0x52f16438dfe0 (libc.so,0x19526)
#09: pc 0x562c98937eaa sp 0x52f16438dff0 (libc.so,0x90eaa)
#10: pc 0 sp 0x52f16438e000
[00057.643] 03530.03702> [3:767060543:0922/211519.707067:57643068:ERROR:sequenced_worker_pool.cc(1373)] shutdown_called_=0
[00057.649] 03530.03655> [3:767583713:0922/211519.712949:57648926:ERROR:sequenced_worker_pool.cc(1373)] shutdown_called_=0
[00057.657] 03530.03557> [341/4670] FrameConnectedBluetoothDevicesTest.DestroyedByWebContentsImplDestruction (150 ms)
[00057.657] 03530.03557> [342/4670] BrowserAssociatedInterfaceTest.Basic (358 ms)
[00057.658] 03530.03557> [343/4670] BrowserMainLoopTest.CreateThreadsInSingleProcess (48 ms)
[00057.658] 03530.03557> [ RUN      ] BrowserThreadTest.PostTask
[00057.659] 03530.03557> [344/4670] BrowserThreadTest.PostTask (CRASHED)
...


This was run via tools/fuchsia/run-swarmed.py so no trybot. But the code in question was trunk + LOGs. (For the record, this is the code that was run https://chromium-review.googlesource.com/c/chromium/src/+/673583/5 .)

I've only seen it once in ~1000 runs so very rare. But also a bit scary given the test that crashed and where it did so.