Web Animations API: Add use counter for Element.animate

Adds one Feature to UseCounter for each version of Element.animate().

More Features will need to be added as Element.animate() expands.

BUG=352490,352491

Review URL: https://codereview.chromium.org/198693002

git-svn-id: svn://svn.chromium.org/blink/trunk@169323 bbb929c8-8fbe-4397-9dbb-9b2b20218538