[Sheriff] Disable timeline-paint/timeline-paint.js on MAC

TBR=petermarshall@chromium.org

No-Try: True
Bug: 1107944
Change-Id: Ib1439afe4f9431ff3855d4db39b7de007a9a5d0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2320173Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791805}

third_party/blink/web_tests/TestExpectations

@@ -6886,3 +6886,6 @@ crbug.com/1046784 [ Linux ] http/tests/devtools/tracing/timeline-misc/timeline-e
 # Sheriff 2020-07-23
 crbug.com/1108728 [ Mac ] external/wpt/html/cross-origin-opener-policy/reporting/access-reporting/opener-accessed_openee-coop-ro.https.html [ Failure ]
 crbug.com/1108786 [ Mac ] http/tests/devtools/tracing/timeline-js/timeline-gc-event.js [ Pass Failure ]
+
+# Sheriff 2020-07-27
+crbug.com/1107944 [ Mac ] http/tests/devtools/tracing/timeline-paint/timeline-paint.js [ Pass Failure ]