Intermittent timeout in /FileAPI/blob/Blob-XHR-revoke.html

[jdm]

  ▶ TIMEOUT [expected CRASH] /FileAPI/blob/Blob-XHR-revoke.html
  │ 
  │ VMware, Inc.
  │ Gallium 0.4 on softpipe
  │ 3.3 (Core Profile) Mesa 12.0.1
  │ Unimplemented scheme for Fetch (thread fetch thread for blob:http://web-platform.test:8000/e1ed9529ba39493ca258fd94f76dd53c, at /Users/servo/buildbot/slave/mac-rel-wpt1/build/components/net/fetch/methods.rs:454)
  │ stack backtrace:
  │    0:        0x10adbe32e - backtrace::backtrace::trace::h0e60ef08c7c34e9f
  │    1:        0x10adbe61c - backtrace::capture::Backtrace::new::h8bf319c36d8f5d1b
  │    2:        0x10aaca9e4 - servo::main::_{{closure}}::h8b62e16079c4851a
  │    3:        0x10c3f56c3 - std::panicking::rust_panic_with_hook::hb1322e5f2588b4db
  │    4:        0x10c0dbda4 - std::panicking::begin_panic::h0914615a412ba184
  │    5:        0x10c1c4b6e - net::fetch::methods::basic_fetch::h64046678e41b4027
  │    6:        0x10c1c2043 - net::fetch::methods::main_fetch::h505cbe6ed186e0b1
  │    7:        0x10c1c139d - net::fetch::methods::fetch_with_cors_cache::hbcb06dac22c7d6f7
  │    8:        0x10c0dedfb - std::panicking::try::do_call::h3f111ff4e3a732ac
  │    9:        0x10c3f69ca - __rust_maybe_catch_panic
  │   10:        0x10c11e776 - _<F as alloc..boxed..FnBox<A>>::call_box::h777cca0df83e2d20
  │   11:        0x10c3f45e4 - std::sys::thread::Thread::new::thread_start::h022e3887023c6290
  │   12:     0x7fff93411059 - _pthread_body
  │   13:     0x7fff93410fd6 - _pthread_start
  │ ERROR:servo: Unimplemented scheme for Fetch
  │ Pipeline failed in hard-fail mode.  Crashing!
  │ servo(62773,0x119f56000) malloc: *** error for object 0x7fb25f8d9bc0: pointer being freed was not allocated
  │ *** set a breakpoint in malloc_error_break to debug
  │ thread panicked while processing panic. aborting.
  └ thread panicked while processing panic. aborting.

This is another instance of the general problem that wptrunner has with recognizing crashes on Mac. Sometimes it doesn't see that the process is dead by the time the timeout is hit.