NetworkService: Add some flaky layout tests to FlagExpectations

From flakiness dashboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&showFlaky=true&builder=chromium.fyi%3AMojo%20Linux

There're more, but adding a few ones that often show flakes (which is
confusing while looking into other flaky issues)

TBR=jam@chromium.org
NOTRY=true

Bug: 729849
Change-Id: I1d862a944f7e1c3a5b792f9783ae56b31ddfdeed
Reviewed-on: https://chromium-review.googlesource.com/746053Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512787}

third_party/WebKit/LayoutTests/FlagExpectations/enable-features=NetworkService

@@ -48,6 +48,17 @@ Bug(none) external/wpt/service-workers/service-worker/shared-worker-controlled.h
 Bug(none) external/wpt/service-workers/service-worker/update-bytecheck.https.html [ Pass Timeout Failure ]
 Bug(none) external/wpt/service-workers/service-worker/worker-interception.https.html [ Pass Crash Failure ]
 Bug(none) external/wpt/service-workers/service-worker/navigation-preload/broken-chunked-encoding.https.html [ Failure ]
+Bug(none) external/wpt/service-workers/service-worker/ServiceWorkerGlobalScope/registration-attribute.https.html [ Pass Failure ]
+Bug(none) external/wpt/service-workers/service-worker/ServiceWorkerGlobalScope/unregister.https.html [ Pass Failure ]
+Bug(none) external/wpt/service-workers/service-worker/appcache-ordering-main.https.html [ Pass Failure ]
+Bug(none) external/wpt/service-workers/service-worker/ready.https.html [ Pass Crash Failure ]
+Bug(none) http/tests/appcache/top-frame-3.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/top-frame-4.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/local-content.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/offline-access.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/foreign-fallback.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/main-resource-redirect.html [ Pass Timeout ]
+Bug(none) http/tests/appcache/reload.html [ Pass Timeout ]
 
 # NetworkService won't support Foreign Fetch.
 Bug(wontfix) external/wpt/service-workers/service-worker/foreign-fetch-basics.https.html [ Skip ]