Intermittent crash in /html/webappapis/idle-callbacks/idlharness.html

[jdm]

▶ CRASH [expected OK] /html/webappapis/idle-callbacks/idlharness.html
  │ 
  │ VMware, Inc.
  │ Gallium 0.4 on softpipe
  │ 3.3 (Core Profile) Mesa 12.0.1
  │ callback not yet supported
  │ Stack trace for thread "ScriptThread PipelineId { namespace_id: PipelineNamespaceId(0), index: PipelineIndex(1) }"
  │ stack backtrace:
  │    0:     0x7fdb69ac4b3d - backtrace::backtrace::trace::he26d3ea809136443
  │    1:     0x7fdb69ac5212 - backtrace::capture::Backtrace::new::hd6fb6e83f9059b0d
  │    2:     0x7fdb68c3f504 - servo::install_crash_handler::handler::hb60740328a53f0c4
  │    3:     0x7fdb6a1be933 - AsmJSFaultHandler
  │                         at /home/servo/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/f7917c4/mozjs/js/src/asmjs/WasmSignalHandlers.cpp:1171
  │    4:     0x7fdb66b2532f - <unknown>
  │    5:     0x7fdb6b492de0 - <unknown>
  │ Stack trace for thread "ScriptThread PipelineId { namespace_id: PipelineNamespaceId(0), index: PipelineIndex(1) }"
  │ stack backtrace:
  │    0:     0x7fdb69ac4b3d - backtrace::backtrace::trace::he26d3ea809136443
  │    1:     0x7fdb69ac5212 - backtrace::capture::Backtrace::new::hd6fb6e83f9059b0d
  │    2:     0x7fdb68c3f504 - servo::install_crash_handler::handler::hb60740328a53f0c4
  │    3:     0x7fdb66570caf - <unknown>
  │    4:     0x7fdb68c3f58f - servo::install_crash_handler::handler::hb60740328a53f0c4
  │    5:     0x7fdb6a1be933 - AsmJSFaultHandler
  │                         at /home/servo/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/f7917c4/mozjs/js/src/asmjs/WasmSignalHandlers.cpp:1171
  │    6:     0x7fdb66b2532f - <unknown>
  └    7:     0x7fdb6b492de0 - <unknown>

[jdm]

Tracking this non-test-specific problem in #19937.