Mark serviceworker-notification-properties as flaky.

Continuing to fail even after being marked 'Slow', so perhaps it's
just plain flaky.

Bug: 1003715
TBR: rockot@chromium.org
Change-Id: I1cdd747b59976929e85a0689d32848d5ea6cc648
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1830110
Commit-Queue: Frank Liberato <liberato@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701306}

third_party/blink/web_tests/SlowTests

@@ -664,7 +664,5 @@ crbug.com/984003 http/tests/virtual-scroller/find-element-65-10px.html [ Slow ]
 crbug.com/984003 http/tests/virtual-scroller/find-element-66-0px.html [ Slow ]
 crbug.com/984003 http/tests/virtual-scroller/find-element-66-10px.html [ Slow ]
 
-crbug.com/1003715 [ Win10 ] http/tests/notifications/serviceworker-notification-properties.html [ Slow ]
-
 # Slow when using Vulkan.
 crbug.com/994331 compositing/lots-of-img-layers.html [ Slow ]

third_party/blink/web_tests/TestExpectations

@@ -6229,3 +6229,5 @@ crbug.com/1008826 [ Mac10.13 ] http/tests/security/frameNavigation/xss-ALLOWED-p
 
 # Sheriff 2019-09-30
 crbug.com/1009016 [ Win10 ] http/tests/devtools/portals/portals-elements-nesting-after-adoption.js [ Pass Failure ]
+crbug.com/1003715 [ Win10 ] http/tests/notifications/serviceworker-notification-properties.html [ Pass Failure ]
+