Animation: Pass fill information to compositor

This sends fill information to the compositor to fix an issue where the compositor was behaving incorrectly when a start delay was specified. Removed WEB_ANIMATION_SUPPORTS_FRACTIONAL_ITERATIONS since it is no longer used.

BUG=415241

Review URL: https://codereview.chromium.org/579043002

git-svn-id: svn://svn.chromium.org/blink/trunk@182537 bbb929c8-8fbe-4397-9dbb-9b2b20218538