The Site Settings subpages should probably use something like <iron-list> to be more performant. Even though they aren't created on page load, instantiating them takes long enough to cause significant stutter on a crazy-powerful desktop.

After creating an empty profile and visiting a dozen websites (to accumulate cookies):

1. Open chrome://md-settings/siteSettings
2. Click Cookies

In a sample run, the animation begins at about 45fps for 20ms, then one 88ms frame followed by a 440ms frame, after which the animation is already over.