Mark service-worker/registration-schedule-job.https.html flaky

TBR=nhiroki@chromium.org

No-Try: true
Bug: 979593
Change-Id: I24b412334c6fe64338bc2e0e3b467c0e8d5f12cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681874
Reviewed-by: Ella Ge <eirage@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673346}

third_party/blink/web_tests/TestExpectations

@@ -6082,3 +6082,7 @@ crbug.com/979336 [ Mac ] fast/dynamic/anonymous-block-orphaned-lines.html [ Pass
 
 # Sheriff 2019-06-28
 crbug.com/979565 [ Mac ] virtual/focusless-spat-nav/fast/spatial-navigation/focusless/snav-focusless-fullscreen-video.html [ Pass Failure ]
+crbug.com/979593 [ Linux Win ] external/wpt/service-workers/service-worker/registration-schedule-job.https.html [ Pass Failure ]
+crbug.com/979593 [ Linux Win ] virtual/blink-cors/external/wpt/service-workers/service-worker/registration-schedule-job.https.html [ Pass Failure ]
+crbug.com/979593 [ Linux Win ] virtual/not-omt-sw-fetch/external/wpt/service-workers/service-worker/registration-schedule-job.https.html [ Pass Failure ]
+crbug.com/979593 [ Linux Win ] virtual/omt-worker-fetch/external/wpt/service-workers/service-worker/registration-schedule-job.https.html [ Pass Failure ]