Skip Web Notification layout tests which will break due to test runner changes.

BUG=349015
R=mvanouwerkerk@chromium.org

Review URL: https://codereview.chromium.org/183683018

git-svn-id: svn://svn.chromium.org/blink/trunk@168485 bbb929c8-8fbe-4397-9dbb-9b2b20218538