Mark a flaky test on Mac10.13.

Bug: 1026712
Change-Id: I3de05d154bf0460c4876b9142dc3b6013927e167
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999544
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731791}

third_party/blink/web_tests/TestExpectations

@@ -6281,6 +6281,7 @@ crbug.com/1034374 http/tests/devtools/tracing/timeline-worker-events.js [ Pass F
 crbug.com/1034374 virtual/threaded/http/tests/devtools/tracing/timeline-worker-events.js [ Pass Failure ]
 crbug.com/1034513 [ Win7 ] virtual/stable/fast/dom/Window/window-resize-contents.html [ Pass Failure ]
 crbug.com/1026712 [ Mac ] fast/forms/time-multiple-fields/time-multiple-fields-stepup-stepdown-from-renderer-hour.html [ Pass Timeout ]
+crbug.com/1026712 [ Mac ] virtual/form-controls-refresh-disabled/fast/forms/time-multiple-fields/time-multiple-fields-stepup-stepdown-from-renderer-hour.html [ Pass Timeout ]
 
 # The Wasm code cache requires disabling the baseline compiler, so only the
 # virtual test should be run.