Web Animations: Remove dependency on legacy comparison functions

As this has a potential to impact performance when evaluating transition
conditions, this patch is being landed in advance of the full removal so that
we can evaluate results on the perf bots.

BUG=334225

Review URL: https://codereview.chromium.org/146003004

git-svn-id: svn://svn.chromium.org/blink/trunk@165716 bbb929c8-8fbe-4397-9dbb-9b2b20218538