Web Animations: Move servicing logic from FrameView to Document

When running animations on the compositor we won't be receiving regular
frame callbacks and will need to trigger servicing separately, for
example to satisfy getComputedStyle.

Review URL: https://codereview.chromium.org/71213002

git-svn-id: svn://svn.chromium.org/blink/trunk@161892 bbb929c8-8fbe-4397-9dbb-9b2b20218538