Mark fast/canvas/canvas-composite-shadow.html flaky on win under oop-r

The test is flaky under oop-r:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=blink_web_tests&tests=virtual%2Foopr-canvas2d%2Ffast%2Fcanvas%2Fcanvas-composite-shadow.html

TBR=kylechar@chromium.org
Bug: 1152496

Change-Id: I8fd1a32544880d899bcfd4c29e10e117de9c08a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2556570Reviewed-by: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830641}

third_party/blink/web_tests/TestExpectations

@@ -6027,5 +6027,6 @@ crbug.com/1149734 http/tests/devtools/sources/debugger-frameworks/frameworks-sou
 crbug.com/1149734 http/tests/devtools/sources/debugger-ui/continue-to-location-markers.js [ Pass Failure ]
 
 #Sheriff 2020-11-24
+crbug.com/1152496 [ Win ] virtual/oopr-canvas2d/fast/canvas/canvas-composite-shadow.html [ Pass Timeout ]
 crbug.com/1087242 http/tests/inspector-protocol/service-worker/network-extrainfo-main-request.js [ Pass Failure Timeout Crash ]
-crbug.com/1149771 [ Linux ] virtual/android/fullscreen/video-scrolled-iframe.html [ Pass Timeout ]
+crbug.com/1149771 [ Linux ] virtual/android/fullscreen/video-scrolled-iframe.html [ Pass Timeout ]
\ No newline at end of file