Gardening: Suppress serviceworker tests timing out on WinXP after r183502

BUG=422278
TBR=horo,eseidel

Review URL: https://codereview.chromium.org/645893002

git-svn-id: svn://svn.chromium.org/blink/trunk@183537 bbb929c8-8fbe-4397-9dbb-9b2b20218538