Intermittent crash in /css21_dev/html4/padding-left-071.htm, /css-text-3_dev/html/css3-text-line-break-opclns-206.htm, and /html/dom/elements/global-attributes/dir_auto-textarea-N-EN.html ("Connection reset by peer" in FontCacheThread::last_resort_font_template)

[jdm]

  ▶ CRASH [expected PASS] /css21_dev/html4/padding-left-071.htm
  │ 
  │ VMware, Inc.
  │ Gallium 0.4 on softpipe
  │ 3.3 (Core Profile) Mesa 12.0.1
  │ failed to receive response to font request: IoError(Error { repr: Os { code: 104, message: "Connection reset by peer" } }) (thread LayoutWorker worker 1/12, at ../src/libcore/result.rs:799)
  │ stack backtrace:
  │    0:     0x7fe87c18b0ed - backtrace::backtrace::trace::h0e60ef08c7c34e9f
  │    1:     0x7fe87c18b772 - backtrace::capture::Backtrace::new::h8bf319c36d8f5d1b
  │    2:     0x7fe87acd242d - servo::main::_{{closure}}::h911afab4cc009f33
  │    3:     0x7fe87c769925 - std::panicking::rust_panic_with_hook::hb1322e5f2588b4db
  │    4:     0x7fe87c7697f2 - std::panicking::begin_panic::hfbeda5aad583dc32
  │    5:     0x7fe87c769730 - std::panicking::begin_panic_fmt::h4fe9fb9d5109c4bf
  │    6:     0x7fe87c7696b1 - rust_begin_unwind
  │    7:     0x7fe87c7a613c - core::panicking::panic_fmt::h4395919ece15c671
  │    8:     0x7fe87bf33ca4 - core::result::unwrap_failed::h3191a47cbfbe2a26
  │    9:     0x7fe87bf56f0d - gfx::font_cache_thread::FontCacheThread::last_resort_font_template::h8a4d8be01d183c59
  │   10:     0x7fe87bf58614 - gfx::font_context::FontContext::layout_font_group_for_style::h01f9ffa61c2005ba
  │   11:     0x7fe87be6113e - layout::text::TextRunScanner::scan_for_runs::h6d421cd1fda9eb14
  │   12:     0x7fe87b0188a5 - _<layout..construct..FlowConstructor<'a, ConcreteThreadSafeLayoutNode>>::build_flow_for_block_starting_with_fragments::hd906ade571a4fd88
  │   13:     0x7fe87b016e14 - _<layout..construct..FlowConstructor<'a, ConcreteThreadSafeLayoutNode>>::build_flow_for_block_like::h6b4d6558251c3ea9
  │   14:     0x7fe87b0161aa - _<layout..construct..FlowConstructor<'a, ConcreteThreadSafeLayoutNode>>::build_flow_for_block::h16765789fa64448a
  │   15:     0x7fe87afab07e - _<layout..construct..FlowConstructor<'a, ConcreteThreadSafeLayoutNode> as layout..traversal..PostorderNodeMutTraversal<ConcreteThreadSafeLayoutNode>>::process::h7eeb4729e86dc15d
  │   16:     0x7fe87af9b978 - _<layout..traversal..RecalcStyleAndConstructFlows<'lc> as style..traversal..DomTraversalContext<N>>::process_postorder::h77e804e07a6927fb
  │   17:     0x7fe87aff9f97 - style::parallel::top_down_dom::ha6ba301686f4e280
  │   18:     0x7fe87b0137b3 - _<std..panic..AssertUnwindSafe<F> as core..ops..FnOnce<()>>::call_once::h92e6ab92d967950b
  │   19:     0x7fe87afc06f0 - std::panicking::try::do_call::h61ee89652c7f18dc
  │   20:     0x7fe87c7722a6 - __rust_maybe_catch_panic
  │   21:     0x7fe87afe7e6c - _<F as alloc..boxed..FnBox<A>>::call_box::h0444ca8d98004df8
  │   22:     0x7fe87c767f60 - std::sys::thread::Thread::new::thread_start::h022e3887023c6290
  │   23:     0x7fe878bdc183 - start_thread
  │   24:     0x7fe8786f337c - clone
  │   25:                0x0 - <unknown>
  │ ERROR:servo: failed to receive response to font request: IoError(Error { repr: Os { code: 104, message: "Connection reset by peer" } })
  └ Pipeline failed in hard-fail mode.  Crashing!

Same symptom as #12872.