Intermittent panic in WebrenderIpcSender::generate_image_key (error receiving image key result: Disconnected)

[CYBAI]

  ▶ TIMEOUT [expected OK] /referrer-policy/gen/iframe.meta/unsafe-url/img-tag/same-http.no-redirect.http.html
  │ 
  │ 
  │ 
  │ 
  │ error receiving image key result: Disconnected (thread <unnamed>, at components/net_traits/lib.rs:778)
  │ stack backtrace:
  │    0: servo::backtrace::print
  │    1: servo::main::{{closure}}
  │    2: std::panicking::rust_panic_with_hook
  │              at src/libstd/panicking.rs:513
  │    3: rust_begin_unwind
  │              at src/libstd/panicking.rs:417
  │    4: core::panicking::panic_fmt
  │              at src/libcore/panicking.rs:111
  │    5: core::option::expect_none_failed
  │              at src/libcore/option.rs:1211
  │    6: net_traits::WebrenderIpcSender::generate_image_key
  │    7: net::image_cache::set_webrender_image_key
  │    8: _ZN3net11image_cache15ImageCacheStore13complete_load17h4b5c03ae9e856cf7E.llvm.16132808074845649456
  │    9: std::sys_common::backtrace::__rust_begin_short_backtrace
  │   10: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   11: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/45ebd5808afd3df7ba842797c0fcd4447ddf30fb/src/liballoc/boxed.rs:1017
  │   12: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/45ebd5808afd3df7ba842797c0fcd4447ddf30fb/src/liballoc/boxed.rs:1017
  │       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:80
  │   13: start_thread
  │   14: __clone
  └ [2020-03-17T01:36:19Z ERROR servo] error receiving image key result: Disconnected
  ▶ Unexpected subtest result in /referrer-policy/gen/iframe.meta/unsafe-url/img-tag/same-http.no-redirect.http.html:
  │ TIMEOUT [expected FAIL] Referrer Policy: Expects stripped-referrer for img-tag to same-http origin and no-redirect redirection from http context.
  └   → Test timed out

[jdm]

This is another instance of servo/ipc-channel#252.