Intermittent GC crash during postMessage in /html/dom/idlharness.worker.html

[jdm]

  ▶ CRASH [expected OK] /html/dom/idlharness.worker.html
  │ 
  │ _RegisterApplication(), FAILED TO establish the default connection to the WindowServer, _CGSDefaultConnection() is NULL.
  │ 
  │ 
  │ 
  │ Stack trace for thread "WebWorker for http://web-platform.test:8000/html/dom/idlharness.worker.js"
  │ stack backtrace:
  │    0: <servo::backtrace::Print as core::fmt::Debug>::fmt
  │    1: core::fmt::write
  │    2: <std::io::stdio::Stdout as std::io::Write>::write_fmt
  │    3: std::io::stdio::_print
  │    4: servo::backtrace::print
  │    5: servo::install_crash_handler::handler
  │    6: _sigtramp
  │    7: _ZN2js15MapGCThingTypedIZNS_14TenuringTracer8traverseIN2JS5ValueEEEvPT_EUlS5_E_EEDaRKS4_OS5_
  │    8: _ZN2js2gc11StoreBuffer14MonoTypeBufferINS1_9ValueEdgeEE5traceERNS_14TenuringTracerE
  │    9: _ZN2js7Nursery12doCollectionEN2JS8GCReasonERNS_2gc16TenureCountCacheE
  │   10: _ZN2js7Nursery7collectEN2JS8GCReasonE
  │   11: _ZN2js2gc9GCRuntime7minorGCEN2JS8GCReasonENS_7gcstats9PhaseKindE
  │   12: _ZN2js14AllocateObjectILNS_7AllowGCE1EEEP8JSObjectP9JSContextNS_2gc9AllocKindEmNS6_11InitialHeapEPKNS_5ClassE
  │   13: _ZN2js11ArrayObject11createArrayEP9JSContextNS_2gc9AllocKindENS3_11InitialHeapEN2JS6HandleIPNS_5ShapeEEENS7_IPNS_11ObjectGroupEEEjRNS_24AutoSetNewObjectMetadataE
  │   14: _ZN2js27NewDenseFullyAllocatedArrayEP9JSContextjN2JS6HandleIP8JSObjectEENS_13NewObjectKindE
  │   15: script::dom::bindings::structuredclone::write
  │   16: _ZN6script3dom26dedicatedworkerglobalscope26DedicatedWorkerGlobalScope17post_message_impl17h209bb2c59f526455E.llvm.500965535905749603
  │   17: <script::dom::dedicatedworkerglobalscope::DedicatedWorkerGlobalScope as script::dom::bindings::codegen::Bindings::DedicatedWorkerGlobalScopeBinding::DedicatedWorkerGlobalScopeBinding::DedicatedWorkerGlobalScopeMethods>::PostMessage_
  │   18: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  │   19: _ZN3std9panicking3try7do_call17h6cac3b08eff9df64E.llvm.15489554176225822398
  │   20: __rust_maybe_catch_panic
  │   21: script::dom::bindings::codegen::Bindings::DedicatedWorkerGlobalScopeBinding::DedicatedWorkerGlobalScopeBinding::postMessage

[jdm]

It might be easier to reproduce problems like this by fixing #24069.

[jdm]

Also happens with a backtrace that suggests it's not in postMessage:

  ▶ CRASH [expected OK] /html/dom/idlharness.worker.html
  │ 
  │ 
  │ 
  │ 
  │ Stack trace for thread "WebWorker for http://web-platform.test:8000/html/dom/idlharness.worker.js"
  │ stack backtrace:
  │    0: <servo::backtrace::Print as core::fmt::Debug>::fmt
  │    1: core::fmt::write
  │    2: <std::io::stdio::Stdout as std::io::Write>::write_fmt
  │    3: std::io::stdio::_print
  │    4: servo::backtrace::print
  │    5: servo::install_crash_handler::handler
  │    6: _sigtramp
  │    7: _ZN2js15MapGCThingTypedIZNS_14TenuringTracer8traverseIN2JS5ValueEEEvPT_EUlS5_E_EEDaRKS4_OS5_
  │    8: _ZN2js2gc11StoreBuffer14MonoTypeBufferINS1_9ValueEdgeEE5traceERNS_14TenuringTracerE
  │    9: _ZN2js7Nursery12doCollectionEN2JS8GCReasonERNS_2gc16TenureCountCacheE
  │   10: _ZN2js7Nursery7collectEN2JS8GCReasonE
  │   11: _ZN2js2gc9GCRuntime7minorGCEN2JS8GCReasonENS_7gcstats9PhaseKindE
  │   12: _ZN2js14AllocateObjectILNS_7AllowGCE1EEEP8JSObjectP9JSContextNS_2gc9AllocKindEmNS6_11InitialHeapEPKNS_5ClassE
  │   13: _ZN2js12NativeObject6createEP9JSContextNS_2gc9AllocKindENS3_11InitialHeapEN2JS6HandleIPNS_5ShapeEEENS7_IPNS_11ObjectGroupEEE
  │   14: _ZL9NewObjectP9JSContextN2JS6HandleIPN2js11ObjectGroupEEENS3_2gc9AllocKindENS3_13NewObjectKindEj
  │   15: _ZN2js29NewObjectWithClassProtoCommonEP9JSContextPKNS_5ClassEN2JS6HandleIP8JSObjectEENS_2gc9AllocKindENS_13NewObjectKindE
  │   16: _ZN2js11RegExpAllocEP9JSContextNS_13NewObjectKindEN2JS6HandleIP8JSObjectEE
  │   17: _ZN2js16regexp_constructEP9JSContextjPN2JS5ValueE