Gardening: Mark fetch-cors-xhr.html on Windows.

This is marked for XP but Win7 tests are also timing-out.

BUG=422278
TBR=horo@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/698723002

git-svn-id: svn://svn.chromium.org/blink/trunk@184760 bbb929c8-8fbe-4397-9dbb-9b2b20218538