Intermittent crash in /_webgl/conformance2/canvas/to-data-url-with-pack-params.html

[jdm]

  ▶ CRASH [expected OK] /_webgl/conformance2/canvas/to-data-url-with-pack-params.html
  │ 
  │ error: XDG_RUNTIME_DIR not set in the environment.
  │ libEGL warning: No hardware driver found, falling back to software rendering
  │ [2020-06-17T16:12:53Z ERROR canvas::webgl_thread] Last GL operation failed: ReadPixels(Rect(300x150 at (0, 0)), 6408, 5121, IpcBytesSender { os_sender: OsIpcSender { fd: SharedFileDescriptor(212), nosync_marker: PhantomData } })
  │ Unexpected WebGL error: 0x502 (1282) [ReadPixels(Rect(300x150 at (0, 0)), 6408, 5121, IpcBytesSender { os_sender: OsIpcSender { fd: SharedFileDescriptor(212), nosync_marker: PhantomData } })] (thread WebGL thread, at components/canvas/webgl_thread.rs:2241)
  │    0: servo::backtrace::print
  │    1: servo::main::{{closure}}
  │    2: std::panicking::rust_panic_with_hook
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/libstd/panicking.rs:481
  │    3: rust_begin_unwind
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/libstd/panicking.rs:385
  │    4: std::panicking::begin_panic_fmt
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/libstd/panicking.rs:339
  │    5: canvas::webgl_thread::WebGLImpl::apply
  │    6: canvas::webgl_thread::WebGLThread::handle_msg
  │    7: canvas::webgl_thread::WebGLThread::process
  │    8: std::sys_common::backtrace::__rust_begin_short_backtrace
  │    9: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   10: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/liballoc/boxed.rs:1034
  │       <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/liballoc/boxed.rs:1034
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at /rustc/a74d1862d4d87a56244958416fd05976c58ca1a8/src/libstd/sys/unix/thread.rs:87
  │   11: start_thread
  │   12: __clone