ProfileBrowserTest.OffTheRecordURLRequestContextIsolation is flaky:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=network_service_browser_tests&tests=ProfileBrowserTest.OffTheRecordURLRequestContextIsolation

Here's a trace of when it fails:
[ RUN      ] ProfileBrowserTest.OffTheRecordURLRequestContextIsolation
Xlib:  extension "RANDR" missing on display ":99".
[31371:31409:0706/104839.212298:ERROR:bus.cc(394)] Failed to connect to the bus: Could not parse server address: Unknown address type (examples of valid types are "tcp" and on UNIX "unix")
[31371:31371:0706/104839.232402:WARNING:password_store_factory.cc(250)] Using basic (unencrypted) store for password storage. See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_password_storage.md for more information about password storage options.
[31406:31458:0706/104840.166229:WARNING:file_path_watcher_linux.cc(656)] Watch failed for /etc/../run/resolvconf: No such file or directory (2)
[31407:31407:0706/104840.178763:WARNING:owning_audio_manager_accessor.cc(80)] Out of process audio service initializing.
[31406:31448:0706/104840.218907:WARNING:pref_notifier_impl.cc(28)] Init observer found at shutdown.
BrowserTestBase received signal: Segmentation fault. Backtrace:
#0 0x0000f7553f67 base::debug::StackTrace::StackTrace()
#1 0x0000f72243a2 base::debug::StackTrace::StackTrace()
#2 0x00000eb8bcd1 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#3 0x0000f76ddcb0 ([vdso]+0xcaf)
#4 0x000008565256 scoped_refptr<>::scoped_refptr<>()
#5 0x00000857edba base::internal::CallbackBase::CallbackBase()
#6 0x00000857ed6a base::OnceCallback<>::OnceCallback()
#7 0x0000085aefff _ZNO4base12OnceCallbackIFvvEE3RunEv
#8 0x000012635d27 download::DownloadServiceImpl::OnControllerInitialized()
#9 0x0000085908fa _ZN4base8internal13FunctorTraitsIM25RenderViewContextMenuBaseFvvEvE6InvokeIS4_P21RenderViewContextMenuJEEEvT_OT0_DpOT1_
#10 0x000008590824 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIM25RenderViewContextMenuBaseFvvEJP21RenderViewContextMenuEEEvOT_DpOT0_
#11 0x00001263773a _ZN4base8internal7InvokerINS0_9BindStateIMN8download19DownloadServiceImplEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLj0EEEEvOT_OT0_NSF_16integer_sequenceIjJXspT1_EEEE
#12 0x000012637621 _ZN4base8internal7InvokerINS0_9BindStateIMN8download19DownloadServiceImplEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#13 0x0000f71d00f8 _ZNO4base12OnceCallbackIFvvEE3RunEv
#14 0x0000f7225c81 base::debug::TaskAnnotator::RunTask()

Because the crash is under "download::DownloadServiceImpl::OnControllerInitialized", I've assigned the "UI>Browser>Downloads" label, but I'm not really sure.