Mark the svg/W3C-I18N/text-anchor tests as flaky on Windows.

TBR=eae@chromium.org
BUG=306691

Review URL: https://codereview.chromium.org/27015003

git-svn-id: svn://svn.chromium.org/blink/trunk@159484 bbb929c8-8fbe-4397-9dbb-9b2b20218538