svg/animations/svglengthlist-animation-3.html no longer flaky

Doesn't appear flaky anymore based on the dashboard.

BUG=350827

Review URL: https://codereview.chromium.org/670723002

git-svn-id: svn://svn.chromium.org/blink/trunk@184087 bbb929c8-8fbe-4397-9dbb-9b2b20218538