Flaky test failing on multiple Mac platforms.

storage_setitem.html

TBR=drott@chromium.org

Bug: 908276
Change-Id: I8bc578f24845a3b0d60bdc3fd9b2de691408ad46
Reviewed-on: https://chromium-review.googlesource.com/c/1349984Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610826}

third_party/blink/web_tests/TestExpectations

@@ -5562,6 +5562,6 @@ crbug.com/906320 [ Mac10.13 ] virtual/not-site-per-process/http/tests/devtools/i
 crbug.com/906320 [ Mac10.13 ] virtual/site-isolated-code-cache/http/tests/devtools/isolated-code-cache/same-origin-test.js [ Failure Pass ]
 
 # Sheriff 2018-11-26
-crbug.com/908276 [ Mac10.10 ] external/wpt/webstorage/storage_setitem.html [ Pass Timeout ]
+crbug.com/908276 [ Mac ] external/wpt/webstorage/storage_setitem.html [ Pass Timeout ]
 crbug.com/908347 [ Mac ] external/wpt/event-timing/event-timing-timingconditions.html [ Failure Pass ]