Mark paint/invalidation/push-block-with-first-line.html is failing on Mac

TBR=wangxianzhu@chromium.org

Bug: 1012638
Change-Id: Ic7af4fd1616459f5858d829c77c502748be5b0f6
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1849490
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704111}

third_party/blink/web_tests/TestExpectations

@@ -6184,3 +6184,7 @@ crbug.com/1011723 virtual/disable-deferred-rendering/fast/canvas/OffscreenCanvas
 # Sheriff 2019-10-04
 crbug.com/1011191 [ Mac ] paint/invalidation/svg/use-clipped-hit.svg  [ Pass Failure ]
 crbug.com/1011188 [ Mac ] paint/invalidation/svg/svg-background-partial-redraw.html [ Pass Failure ]
+
+# Sheriff 2019-10-09
+crbug.com/1012638 [ Mac ] paint/invalidation/push-block-with-first-line.html [ Pass Failure ]
+