Mark http/tests/appcache/remove-cache.html as flaky

This is flaking on the Mac10.13 Tests Debug bot:
https://ci.chromium.org/p/chromium/builders/ci/Mac10.13%20Tests%20%28dbg%29/15476

Bug: 1022915
Change-Id: I03c36b4034b9a96e208ebe3fd683e41765ece25e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1914899
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Auto-Submit: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715075}

third_party/blink/web_tests/TestExpectations

@@ -5887,6 +5887,9 @@ crbug.com/1021407 [ Retina Release ] virtual/audio-service/media/video-controls-
 crbug.com/1021407 [ Mac10.11 ] virtual/audio-service/media/controls/video-overlay-cast-dark-rendering.html [ Pass Failure ]
 crbug.com/1021407 [ Mac10.11 ] media/controls/video-overlay-cast-dark-rendering.html [ Pass Failure ]
 
+# Sheriff 2019-11-13
+crbug.com/1024398 [ Debug ] http/tests/appcache/remove-cache.html [ Pass Failure ]
+
 # Temporarily disabled to land scope changes in DevTools
 crbug.com/963183 http/tests/devtools/sources/debugger-pause/set-return-value.js [ Pass Failure ]
 crbug.com/963183 http/tests/devtools/sources/debugger/debugger-proto-property.js [ Pass Failure ]