sheriff: mark transform-on-large-layer as flaky

Bug: 1131551
Change-Id: Ia0b99ed3a98680c7add4afe2b4f8e104d5689fda
Tbr: enne@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425847Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809865}

third_party/blink/web_tests/TestExpectations

@@ -5583,7 +5583,6 @@ crbug.com/945774 external/wpt/content-security-policy/frame-ancestors/frame-ance
 # Tests using testRunner.useUnfortunateSynchronousResizeMode occasionally timeout,
 # but the test coverage is still good.
 crbug.com/919789 css3/viewport-percentage-lengths/viewport-percentage-lengths-resize.html [ Pass Timeout ]
-crbug.com/919789 compositing/transitions/transform-on-large-layer.html [ Pass Timeout ]
 crbug.com/919789 compositing/transitions/transform-on-large-layer-expected.html [ Pass Timeout ]
 crbug.com/919789 fast/autoresize/turn-off-autoresize.html [ Pass Timeout ]
 crbug.com/919789 fast/autoresize/basic.html [ Pass Timeout ]
@@ -6749,3 +6748,6 @@ crbug.com/1130533 [ Mac ] external/wpt/xhr/xhr-timeout-longtask.any.html [ Pass
 
 # Sheriff 2020-09-22
 crbug.com/1130533 [ Mac ] external/wpt/xhr/xhr-timeout-longtask.any.worker.html [ Pass Failure ]
+
+# Sheriff 2020-09-23
+crbug.com/1131551 compositing/transitions/transform-on-large-layer.html [ Pass Failure Timeout ]