Don't run paused animations on the compositor.

There is a bug where compositable animations are started (and played back)
even if their initial state is "paused".

It would appear that pausing/unpausing composited animations is not
implemented, and that pausing a currently running composited animation
causes it to be permanently "thrown out" of the compositor. In light of
this, I suggest to simply not start paused animations on the compositor,
for now.

BUG=342192
TEST=manual

Review URL: https://codereview.chromium.org/159733003

git-svn-id: svn://svn.chromium.org/blink/trunk@167140 bbb929c8-8fbe-4397-9dbb-9b2b20218538