"Messageport Gc'ed too early" panic in /fetch/security/embedded-credentials.tentative.sub.html

[jdm]

  ▶ CRASH [expected TIMEOUT] /fetch/security/embedded-credentials.tentative.sub.html
  │ 
  │ 
  │ 
  │ 
  │ [2019-11-11T14:02:51Z ERROR servo::browser] Multiple top level browsing contexts not supported yet.
  │ [2019-11-11T14:02:51Z ERROR servo::browser] Multiple top level browsing contexts not supported yet.
  │ [2019-11-11T14:02:51Z ERROR servo::browser] Multiple top level browsing contexts not supported yet.
  │ [2019-11-11T14:02:51Z ERROR servo::browser] Multiple top level browsing contexts not supported yet.
  │ Messageport Gc'ed too early (thread ScriptThread PipelineId { namespace_id: PipelineNamespaceId(1), index: PipelineIndex(1) }, at components/script/dom/globalscope.rs:513)
  │ stack backtrace:
  │    0: servo::main::{{closure}}
  │    1: std::panicking::rust_panic_with_hook
  │              at src/libstd/panicking.rs:472
  │    2: std::panicking::begin_panic
  │    3: script::dom::globalscope::GlobalScope::route_task_to_port
  │    4: <script::dom::globalscope::GlobalScope::start_message_port::process_pending_port_messages<F> as script::task::TaskOnce>::run_once
  │    5: <T as script::task::TaskBox>::run_box
  │    6: script::script_thread::ScriptThread::handle_msg_from_script
  │    7: _ZN6script13script_thread12ScriptThread11handle_msgs17h79a21672632590f6E.llvm.11879425879184375510
  │    8: script::script_thread::ScriptThread::start
  │    9: profile_traits::mem::ProfilerChan::run_with_memory_reporting
  │   10: std::sys_common::backtrace::__rust_begin_short_backtrace
  │   11: _ZN3std9panicking3try7do_call17h1ed362cc121fa29bE.llvm.11737484828325240857
  │   12: __rust_maybe_catch_panic
  │              at src/libpanic_unwind/lib.rs:80
  │   13: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   14: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/246be7e1a557b8ac8287c6842379a0db67770be6/src/liballoc/boxed.rs:942
  │   15: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/246be7e1a557b8ac8287c6842379a0db67770be6/src/liballoc/boxed.rs:942
  │       std::sys_common::thread::start_thread
  │              at src/libstd/sys_common/thread.rs:13
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at src/libstd/sys/unix/thread.rs:79
  │   16: start_thread
  │   17: clone
  │ 
  │ [2019-11-11T14:02:52Z ERROR servo] Messageport Gc'ed too early
  └ Pipeline failed in hard-fail mode.  Crashing!

cc @gterzian
Is this fixed by #24664?

[gterzian]

This is not fixed by #24664.

Here, the global is managing the port, however when the time comes to dispatch a MessageEvent, the corresponding WeakRef<MessagePort> has already been GC'ed

servo/components/script/dom/globalscope.rs

Line 513 in f7fb130

None => panic!("Messageport Gc'ed too early"),