A test added in crrev.com/c/895165 crashes when creating a dedicated worker inside of an iframe with CSP: sandbox header.

Here is the crash trace from the test result:
--
crash log for renderer (pid <unknown>):
STDOUT: #CRASHED - renderer
STDERR: 
STDERR: DevTools listening on ws://127.0.0.1:46805/devtools/browser/585cabfd-6c64-48f6-8d1a-39f68ee87107
STDERR: CONSOLE ERROR: Failed to load https://web-platform.test:8444/service-workers/service-worker/resources/sandboxed-iframe-fetch-event-iframe.py?script_fetch_cors: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
STDERR: [1:22:0201/105012.587235:FATAL:StdLibExtras.h(128)] Check failed: IsNotRacy(allow_cross_thread_use). 
STDERR: #0 0x7f95d044063c base::debug::StackTrace::StackTrace()
STDERR: #1 0x7f95d046aa3c logging::LogMessage::~LogMessage()
STDERR: #2 0x7f95cc8e639d blink::SpaceSplitString::SharedDataMap()
STDERR: #3 0x7f95cc8e5c8c blink::SpaceSplitString::Data::Create()
STDERR: #4 0x7f95cc8e643d blink::SpaceSplitString::Set()
STDERR: #5 0x7f95ccba592f blink::CSPDirectiveList::ApplySandboxPolicy()
STDERR: #6 0x7f95ccba4d31 blink::CSPDirectiveList::AddDirective()
STDERR: #7 0x7f95ccb9f479 blink::CSPDirectiveList::Parse()
STDERR: #8 0x7f95ccb9f1ba blink::CSPDirectiveList::Create()
STDERR: #9 0x7f95ccbadac9 blink::ContentSecurityPolicy::AddPolicyFromHeaderValue()
STDERR: #10 0x7f95ccbad0ad blink::ContentSecurityPolicy::AddAndReportPolicyFromHeaderValue()
STDERR: #11 0x7f95ccbad59e blink::ContentSecurityPolicy::DidReceiveHeader()
STDERR: #12 0x7f95cd384510 blink::WorkerOrWorkletGlobalScope::ApplyContentSecurityPolicyFromVector()
STDERR: #13 0x7f95cd37e50a blink::WorkerGlobalScope::WorkerGlobalScope()
STDERR: #14 0x7f95cd36ae35 blink::DedicatedWorkerGlobalScope::DedicatedWorkerGlobalScope()
STDERR: #15 0x7f95cd36f0b0 blink::DedicatedWorkerThread::CreateWorkerGlobalScope()
STDERR: #16 0x7f95cd388357 blink::WorkerThread::InitializeOnWorkerThread()
STDERR: #17 0x7f95cd38c5a3 _ZN4base8internal7InvokerINS0_9BindStateIMN5blink12WorkerThreadEFvNSt3__110unique_ptrINS3_25GlobalScopeCreationParamsENS5_14default_deleteIS7_EEEERKNS_8OptionalINS3_30WorkerBackingThreadStartupDataEEENS3_20WorkerInspectorProxy18PauseOnWorkerStartEEJN3WTF28CrossThreadUnretainedWrapperIS4_EENSK_13PassedWrapperISA_EESD_SH_EEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #18 0x7f95cb2aac11 blink::(anonymous namespace)::RunCrossThreadClosure()
STDERR: #19 0x7f95cb2ab745 _ZN4base8internal7InvokerINS0_9BindStateIPFvN3WTF19CrossThreadFunctionIFvvEEEEJS6_EEES5_E7RunOnceEPNS0_13BindStateBaseE
STDERR: #20 0x7f95d0440f5a base::debug::TaskAnnotator::RunTask()
STDERR: #21 0x7f95cb59a8ec blink::scheduler::TaskQueueManager::ProcessTaskFromWorkQueue()
STDERR: #22 0x7f95cb599e27 blink::scheduler::TaskQueueManager::DoWork()
STDERR: #23 0x7f95cb59ebd8 _ZN4base8internal7InvokerINS0_9BindStateIMN5blink9scheduler16TaskQueueManagerEFvNS4_8internal8Sequence8WorkTypeEEJNS_7WeakPtrIS5_EES8_EEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #24 0x7f95d0440f5a base::debug::TaskAnnotator::RunTask()
STDERR: #25 0x7f95cb5a0d78 blink::scheduler::internal::ThreadControllerImpl::DoWork()
STDERR: #26 0x7f95cb59ebd8 _ZN4base8internal7InvokerINS0_9BindStateIMN5blink9scheduler16TaskQueueManagerEFvNS4_8internal8Sequence8WorkTypeEEJNS_7WeakPtrIS5_EES8_EEEFvvEE3RunEPNS0_13BindStateBaseE
STDERR: #27 0x7f95d0440f5a base::debug::TaskAnnotator::RunTask()
STDERR: #28 0x7f95d0475516 base::internal::IncomingTaskQueue::RunTask()
STDERR: #29 0x7f95d04797f7 base::MessageLoop::RunTask()
STDERR: #30 0x7f95d0479c14 base::MessageLoop::DeferOrRunPendingTask()
STDERR: #31 0x7f95d0479ed8 base::MessageLoop::DoWork()
STDERR: #32 0x7f95d047b370 base::MessagePumpDefault::Run()
STDERR: #33 0x7f95d047904c base::MessageLoop::Run()
STDERR: #34 0x7f95d04b0cb6 base::RunLoop::Run()
STDERR: #35 0x7f95d04f452a base::Thread::Run()
STDERR: #36 0x7f95d04f4b23 base::Thread::ThreadMain()
STDERR: #37 0x7f95d04eaf6f base::(anonymous namespace)::ThreadFunc()
STDERR: #38 0x7f95d26ca494 start_thread
STDERR: #39 0x7f95c9096a8f clone
STDERR: