Intermittent timeout in /dom/events/webkit-transition-end-event.html

[jdm]

  ▶ TIMEOUT [expected OK] /dom/events/webkit-transition-end-event.html
  │ 
  │ error: XDG_RUNTIME_DIR not set in the environment.
  └ libEGL warning: No hardware driver found, falling back to software rendering
  ▶ Unexpected subtest result in /dom/events/webkit-transition-end-event.html:
  │ TIMEOUT [expected FAIL] webkitTransitionEnd event listener should trigger for an animation
  └   → Test timed out
  ▶ Unexpected subtest result in /dom/events/webkit-transition-end-event.html:
  └ NOTRUN [expected PASS] webkitTransitionEnd event listener should not trigger if an unprefixed listener also exists
  ▶ Unexpected subtest result in /dom/events/webkit-transition-end-event.html:
  └ NOTRUN [expected PASS] webkitTransitionEnd event listener should not trigger if an unprefixed event handler also exists
  ▶ Unexpected subtest result in /dom/events/webkit-transition-end-event.html:
  └ NOTRUN [expected FAIL] event types for prefixed and unprefixed transitionend event listeners should be named appropriately
  ▶ Unexpected subtest result in /dom/events/webkit-transition-end-event.html:
  └ NOTRUN [expected PASS] webkitTransitionEnd event listener is case sensitive

cc @mrobinson