Convert the new WebAnimation objects to the Compositor interface.

Currently working:
    * Opacity support
    * Transform support mostly there in https://codereview.chromium.org/67833002/

Currently missing:
    * Filter support


BUG=

Review URL: https://codereview.chromium.org/63463002

git-svn-id: svn://svn.chromium.org/blink/trunk@161786 bbb929c8-8fbe-4397-9dbb-9b2b20218538