[Sheriff] Mark http/tests/images/document-policy-oversized-images-resize.php as flaky

Bug: 1087208
Change-Id: Iadf7f79f37f27133c8fa1089a15c173142341500
Tbr: dbertoni@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2217760Reviewed-by: Takashi Sakamoto <tasak@google.com>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#772543}

third_party/blink/web_tests/TestExpectations

@@ -5893,3 +5893,6 @@ crbug.com/1086353 [ Win ] http/tests/websocket/close-in-order.html [ Pass Failur
 # Sheriff 2020-05-27
 crbug.com/1083585 [ Win ] geolocation-api/watchPosition-page-visibility.html [ Pass Failure ]
 crbug.com/1046784 http/tests/devtools/elements/styles/stylesheet-tracking.js [ Pass Failure Timeout ]
+
+# Sheriff 2020-05-28
+crbug.com/1087208 http/tests/images/document-policy-oversized-images-resize.php [ Pass Failure ]