Mark http/tests/misc/window-dot-stop.html as flaky

TBR=kinuko@chromium.org

Bug: 869773
Change-Id: I9d38fcdc57d7e240653f85f9df32a964826cd6f4
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1158114Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579726}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4863,3 +4863,6 @@ crbug.com/869364 css3/filters/filter-repaint-composited-fallback.html [ Pass Tim
 crbug.com/869364 external/wpt/IndexedDB/parallel-cursors-upgrade.html [ Pass Timeout ]
 crbug.com/869364 http/tests/devtools/console/console-correct-suggestions.js [ Pass Timeout ]
 crbug.com/869364 virtual/gpu/fast/canvas/OffscreenCanvas-filter.html [ Pass Timeout ]
+
+# Sheriff 2018-08-01
+crbug.com/869773 [ Mac Linux ] http/tests/misc/window-dot-stop.html [ Pass Failure ]