[Sheriff] Mark disable-dimension-attributes as Timeout on Mac and Linux

TBR=jdoerrie@chromium.org

Bug: 999799
Change-Id: Ide8079f28b864e82efe6184b9c54602808075607
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1781643Reviewed-by: Jan Wilken Dörrie <jdoerrie@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692623}

third_party/blink/web_tests/TestExpectations

@@ -6525,3 +6525,6 @@ crbug.com/999473 external/wpt/streams/writable-streams/properties.any.worker.htm
 
 crbug.com/1000051 [ Mac ] virtual/audio-service/media/controls/volume-slider.html [ Failure Timeout Pass ]
 crbug.com/1000124 [ Mac ] compositing/overflow/update-widget-positions-on-nested-frames-and-scrollers.html [ Crash ]
+
+# Sheriff 2019-09-03
+crbug.com/999799 [ Mac Linux ] external/wpt/html/rendering/dimension-attributes.html [ Pass Timeout ]