Update test expectations for virtual/serviceworker/http/tests/serviceworker/postmessage-msgport-to-client.html

It has stopped crashing after chromium r270375:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=virtual%2Fserviceworker%2Fhttp%2Ftests%2Fserviceworker

BUG=372260
TBR=dominicc

Review URL: https://codereview.chromium.org/287153003

git-svn-id: svn://svn.chromium.org/blink/trunk@174147 bbb929c8-8fbe-4397-9dbb-9b2b20218538