Workaround for race condition that only happens on Windows Chrome with
the --enable-web-animations-css flag turned on.

BUG=280439

Review URL: https://chromiumcodereview.appspot.com/23691007

git-svn-id: svn://svn.chromium.org/blink/trunk@157578 bbb929c8-8fbe-4397-9dbb-9b2b20218538