Disable layout test xrSession_requestReferenceSpace_features.https.html

webxr/xrSession_requestReferenceSpace_features.https.html
is flaky on MAC bots Mac10.15 Tests.

TBR=klausw@chromium.org

Bug: 1161301
Change-Id: Ia885d0a6f10ea7c0b9262a9c8d4a886564bf1c66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601066Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838994}

third_party/blink/web_tests/TestExpectations

@@ -5920,3 +5920,4 @@ crbug.com/1046784 http/tests/devtools/console/console-context-selector.js [ Pass
 
 #Sheriff 2020-12-22
 crbug.com/1161244 [ Mac ] external/wpt/html/cross-origin-opener-policy/popup-coop-by-sw-from-coop.https.html [ Pass Timeout ]
+crbug.com/1161301 [ Mac ] external/wpt/webxr/xrSession_requestReferenceSpace_features.https.html [ Pass Timeout ]