Suppress a flaky layout test.

NOTRY=true
BUG=316372
TBR=antonm@chromium.org, kbr@chromium.org

Review URL: https://codereview.chromium.org/61763018

git-svn-id: svn://svn.chromium.org/blink/trunk@161588 bbb929c8-8fbe-4397-9dbb-9b2b20218538