Disable http/tests/devtools/service-workers/service-worker-v8-cache.js on Mojo Linux

It's failing consistently on the Network Service bot, probably due to DCHECK.

Sample Build:
https://ci.chromium.org/buildbot/chromium.fyi/Mojo%20Linux/14273

TBR=falken@chromium.org,horo@chromium.org

Bug: 849670, 789111
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I3d9da983aa3ba2006a75c27639da8e6fe716875c
Reviewed-on: https://chromium-review.googlesource.com/1089356
Commit-Queue: Chong Zhang <chongz@chromium.org>
Reviewed-by: Chong Zhang <chongz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564987}

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

@@ -23,3 +23,6 @@ Bug(none) http/tests/security/powerfulFeatureRestrictions/old-powerful-features-
 # Only passes with Network Servce enabled (unfortunately this expectation still
 # allows Timeout from the top-level exctations though).
 crbug.com/800898 external/wpt/FileAPI/url/url-in-tags-revoke.window.html [ Pass ]
+
+# Flaky on non-NetworkService (disabled), consistent failing on NetworkService. Probably due to DCHECK.
+crbug.com/849670 http/tests/devtools/service-workers/service-worker-v8-cache.js [ Pass Failure ]