Gardening: NeedsRebaseline for http/tests/serviceworker/fetch-event.html

BUG=416371
TBR=horo
NOTRY=true

Review URL: https://codereview.chromium.org/645903002

git-svn-id: svn://svn.chromium.org/blink/trunk@183539 bbb929c8-8fbe-4397-9dbb-9b2b20218538