Add expectation for flaky...

Add expectation for flaky external/wpt/fullscreen/api/element-request-fullscreen-and-remove-manual.html

This test seems to be flaky on multiple bots.

TBR=foolip@chromium.org

Bug: 936827
Change-Id: Id91065f4df77d03721eed2e6f1ca17d2a5f17ac4
Reviewed-on: https://chromium-review.googlesource.com/c/1494875Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Ioana Pandele <ioanap@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636473}

third_party/blink/web_tests/TestExpectations

@@ -5919,3 +5919,6 @@ crbug.com/932078 virtual/outofblink-cors/http/tests/security/powerfulFeatureRest
 
 # Wasm threads enabled by default
 crbug.com/754910 virtual/origin-trials-runtimeflags-disabled/http/tests/origin_trials/webexposed/wasm-threads-origin-trial-disabled.html [ Skip ]
+
+# Sheriff 2019-02-28
+crbug.com/936827 external/wpt/fullscreen/api/element-request-fullscreen-and-remove-manual.html [ Failure Pass ]
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