Update web tests expectations for MacOS 10.14

http/tests/security/frameNavigation/xss-ALLOWED-parent-navigation-change.html
occasionally timeout on MacOS 10.14, adding to TextExpectations.

TBR=wangxianzhu@chromium.org

Bug: 1008826, 1028242
Change-Id: I9b0908a8c89c1915a62d7fe922359927afc2ab6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2032027Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737095}

third_party/blink/web_tests/TestExpectations

@@ -6002,6 +6002,7 @@ crbug.com/1005128 crypto/subtle/abandon-crypto-operation2.html [ Pass Crash ]
 
 # Sheriff 2019-09-27
 crbug.com/1008826 [ Retina ] http/tests/security/frameNavigation/xss-ALLOWED-parent-navigation-change.html [ Pass Failure Timeout ]
+crbug.com/1008826 [ Mac10.14 ] http/tests/security/frameNavigation/xss-ALLOWED-parent-navigation-change.html [ Pass Failure Timeout ]
 
 # Sheriff 2019-09-30
 crbug.com/1003715 [ Win10 ] http/tests/notifications/serviceworker-notification-properties.html [ Pass Failure Timeout ]