Intermittent crash of /css21_dev/html4/ignored-rules-001.htm

[KiChjang]

 ▶ CRASH [expected PASS] /css21_dev/html4/ignored-rules-001.htm
  │ 
  │ VMware, Inc.
  │ Gallium 0.4 on softpipe
  │ 3.3 (Core Profile) Mesa 12.0.1
  │ called `Result::unwrap()` on an `Err` value: IoError(Error { repr: Os { code: 104, message: "Connection reset by peer" } }) (thread main, at ../src/libcore/result.rs:837)
  │ stack backtrace:
  │    0:     0x7f8ddf4f2b1d - backtrace::backtrace::trace::h16372ee7bf1517e5
  │    1:     0x7f8ddf4f31b2 - backtrace::capture::Backtrace::new::hcc43c50c4b11c693
  │    2:     0x7f8ddf05e44d - servo::main::_{{closure}}::hb6cfccd56d2ea374
  │    3:     0x7f8de0cc75c4 - std::panicking::rust_panic_with_hook
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:452
  │    4:     0x7f8de0cc7484 - std::panicking::begin_panic<collections::string::String>
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:413
  │    5:     0x7f8de0cc73a9 - std::panicking::begin_panic_fmt
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:397
  │    6:     0x7f8de0cc7337 - std::panicking::rust_begin_panic
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:373
  │    7:     0x7f8de0d03d9d - core::panicking::panic_fmt
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libcore/panicking.rs:69
  │    8:     0x7f8de0ae4f5f - core::result::unwrap_failed::h97cf4d1c2597280e
  │    9:     0x7f8de0ae7190 - webrender_traits::api::RenderApi::get_scroll_layer_state::h0045dd09d6e6c535
  │   10:     0x7f8ddf04fcf0 - _<compositing..compositor..IOCompositor<Window>>::send_viewport_rects::h9d0e14be735b560a
  │   11:     0x7f8ddf052956 - _<compositing..compositor..IOCompositor<Window>>::handle_browser_message::hddc107467c25949b
  │   12:     0x7f8ddf0404de - _<servo..Browser<Window>>::handle_events::h1df927e02e9ff0e5
  │   13:     0x7f8ddf05d295 - servo::main::h253c85c035fd6cbb
  │   14:     0x7f8de0ccfc2a - panic_unwind::__rust_maybe_catch_panic
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libpanic_unwind/lib.rs:97
  │   15:     0x7f8de0cc65ea - std::panicking::try<(),fn()>
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:332
  │                          - std::panic::catch_unwind<fn(),()>
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/panic.rs:351
  │                          - std::rt::lang_start
  │                         at /buildslave/rust-buildbot/slave/nightly-dist-rustc-linux/build/obj/../src/libstd/rt.rs:57
  │   16:     0x7f8ddc964f44 - __libc_start_main
  │   17:     0x7f8ddf030409 - <unknown>
  │   18:                0x0 - <unknown>
  │ ERROR:servo: called `Result::unwrap()` on an `Err` value: IoError(Error { repr: Os { code: 104, message: "Connection reset by peer" } })
  └ Pipeline failed in hard-fail mode.  Crashing!

[jdm]

Covered by #13479.