Disable flaky test: overlay-persistent-overlays-with-emulation.js

The test is flaky on Win7.
Flaky dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=inspector-protocol%2Foverlay%2Foverlay-persistent-overlays-with-emulation.js&testType=blink_web_tests

TBR=alexrudenko@chromium.org

No-Try: true
Bug: 1154940
Change-Id: Ib153f02efb76026ae8d78b7504aa2f5b424a25e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2569479
Commit-Queue: Asami Doi <asamidoi@chromium.org>
Reviewed-by: Asami Doi <asamidoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833128}

third_party/blink/web_tests/TestExpectations

@@ -5984,3 +5984,7 @@ crbug.com/931646 [ Mac ] http/tests/preload/meta-viewport-link-headers-imagesrcs
 # for waitings in web tests to trigger a detection event.
 crbug.com/1032681 http/tests/subresource_filter/overlay_popup_ad/* [ Skip ]
 crbug.com/1032681 virtual/disable-frequency-capping-for-overlay-popup-detection/http/tests/subresource_filter/overlay_popup_ad/* [ Pass ]
+
+# Sheriff 2020-12-03
+crbug.com/1154940 [ Win7 ] inspector-protocol/overlay/overlay-persistent-overlays-with-emulation.js [ Pass Failure ]
+