Web Animations CSS: Revert back to not wait for compositing update

By ensuring that the pending CSS Animation update is applied before the
new RenderStyle is set on the RenderObject we can participate in the
update of layer compositing state correctly.

Removes changes added in r162401 which serviced animations after a
deferred compositing update and forced layout after the animation
frame callback in the test proxy.

R=steveblock
TBR=abarth
TESTED=manually ran compositing/ and virtual/threaded with --enable-web-animations-css
BUG=298211

Review URL: https://codereview.chromium.org/79823002

git-svn-id: svn://svn.chromium.org/blink/trunk@162469 bbb929c8-8fbe-4397-9dbb-9b2b20218538