Intermittent error in /2dcontext/drawing-images-to-the-canvas/2d.drawImage.path.html, /2dcontext/line-styles/2d.line.join.bevel.html and /2dcontext/transformations/2d.transformation.translate.nonfinite.html

[jdm]

  ▶ ERROR [expected OK] /2dcontext/drawing-images-to-the-canvas/2d.drawImage.path.html
  └   → Traceback (most recent call last):
  File "/Users/servo/buildbot/slave/mac-rel-wpt1/build/tests/wpt/harness/wptrunner/executors/base.py", line 149, in run_test
    result = self.do_test(test)
  File "/Users/servo/buildbot/slave/mac-rel-wpt1/build/tests/wpt/harness/wptrunner/executors/executorservo.py", line 143, in do_test
    self.proc.kill()
  File "/Users/servo/buildbot/slave/mac-rel-wpt1/build/python/_virtualenv/lib/python2.7/site-packages/mozprocess/processhandler.py", line 749, in kill
    self.proc.kill(sig=sig)
  File "/Users/servo/buildbot/slave/mac-rel-wpt1/build/python/_virtualenv/lib/python2.7/site-packages/mozprocess/processhandler.py", line 174, in kill
    send_sig(signal.SIGKILL)
  File "/Users/servo/buildbot/slave/mac-rel-wpt1/build/python/_virtualenv/lib/python2.7/site-packages/mozprocess/processhandler.py", line 152, in send_sig
    os.killpg(pid, sig)
OSError: [Errno 1] Operation not permitted