Mark worklet-animation-with-scroll-timeline flaky on compositor path

See dashboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=worklet-animation-with-scroll-timeline

TBR=treib@chromium.org
NOTRY=true

Bug: 915352
Change-Id: I7b1a586a9352fcb8b3a4a7d8ab838f199c0858b4
Reviewed-on: https://chromium-review.googlesource.com/c/1496763Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636801}

third_party/blink/web_tests/TestExpectations

@@ -5956,7 +5956,7 @@ crbug.com/915352 virtual/threaded/external/wpt/animation-worklet/scroll-timeline
 crbug.com/915352 virtual/threaded/external/wpt/animation-worklet/worklet-animation-pause-resume.https.html [ Pass Failure ]
 crbug.com/915352 virtual/threaded/external/wpt/animation-worklet/worklet-animation-with-fill-mode.https.html [ Pass Failure ]
 
-crbug.com/915352 [ Mac10.11 ] virtual/threaded/external/wpt/animation-worklet/worklet-animation-with-scroll-timeline.https.html [ Failure ]
+crbug.com/915352 [ Mac10.10 Mac10.11 ] virtual/threaded/external/wpt/animation-worklet/worklet-animation-with-scroll-timeline.https.html [ Pass Failure ]
 crbug.com/915352 [ Mac10.10 Mac10.11 ] virtual/threaded/external/wpt/animation-worklet/worklet-animation-with-scroll-timeline-and-display-none.https.html [ Pass Failure ]
 
 # Sheriff 2019-03-01