Intermittent crash in /_webgl/conformance2/query/query.html

[jdm]

▶ CRASH [expected OK] /_webgl/conformance2/query/query.html
  │ 
  │ _RegisterApplication(), FAILED TO establish the default connection to the WindowServer, _CGSDefaultConnection() is NULL.
  │ [2020-06-18T19:10:11Z ERROR canvas::webgl_thread] Last GL operation failed: BeginQuery(35976, WebGLQueryId(1))
  │ Unexpected WebGL error: 0x502 (1282) [BeginQuery(35976, WebGLQueryId(1))] (thread WebGL thread, at components/canvas/webgl_thread.rs:2265)
  │    0: <servo::backtrace::Print as core::fmt::Debug>::fmt
  │    1: core::fmt::write
  │    2: std::io::Write::write_fmt
  │    3: servo::backtrace::print
  │    4: servo::main::{{closure}}
  │    5: std::panicking::rust_panic_with_hook
  │    6: _rust_begin_unwind
  │    7: std::panicking::begin_panic_fmt
  │    8: canvas::webgl_thread::WebGLImpl::apply
  │    9: canvas::webgl_thread::WebGLThread::handle_msg
  │   10: canvas::webgl_thread::WebGLThread::process
  │   11: std::sys_common::backtrace::__rust_begin_short_backtrace
  │   12: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   13: std::sys::unix::thread::Thread::new::thread_start
  │   14: __pthread_body
  │   15: __pthread_start

[jdm]

I'm pretty sure this is a regression from #26922, but I have no idea how.

[jdm]

#26956 as well.