[Sheriff] Mark geolocation-api/watchPosition-page-visibility.html as flaky on Win7.

Bug: 1083585
Change-Id: I5660fbc7cf8ce917013eabd6c2c8d66385baa7f5
Tbr: danakj@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216137Reviewed-by: Takashi Sakamoto <tasak@google.com>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#772098}

third_party/blink/web_tests/TestExpectations

@@ -5879,3 +5879,6 @@ crbug.com/971031 [ Mac ] fast/dom/timer-throttling-hidden-page.html [ Pass Failu
 crbug.com/1071189 [ Debug ] editing/selection/programmatic-selection-on-mac-is-directionless.html [ Timeout Pass ]
 
 crbug.com/1086353 [ Win ] http/tests/websocket/close-in-order.html [ Pass Failure ]
+
+# Sheriff 2020-05-27
+crbug.com/1083585 [ Win7 ] geolocation-api/watchPosition-page-visibility.html [ Pass Failure ]