Mark printing/composited-thead-tfoot-repeat.html flaky on Mac10.13

TBR=wangxianzhu@chromium.org

Bug: 945085
Change-Id: Ibfcfb829b51ea4d97b5f65e1a7f6972a808be789
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536565Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643662}

third_party/blink/web_tests/TestExpectations

@@ -6125,3 +6125,6 @@ crbug.com/943969 [ Win ] inspector-protocol/animation/animation-pause-infinite.j
 crbug.com/943969 [ Mac10.10 Mac10.11 ] inspector-protocol/animation/animation-pause-infinite.js [ Pass Failure ]
 crbug.com/943969 [ Win ] inspector-protocol/css/css-get-media-queries.js [ Pass Failure ]
 crbug.com/943969 [ Mac10.10 Mac10.11 ] inspector-protocol/css/css-get-media-queries.js [ Pass Failure ]
+
+crbug.com/945085 [ Mac10.13 ] printing/composited-thead-tfoot-repeat.html [ Failure Pass ]
+