Revert 171714 - Use an auxiliary list of animation controllers.

Revert 171714 - Use an auxiliary list of animation controllers.

> With this patch we accomplish the following:
>  1. layer animation controllers are ref counted (so they can be shared by the two impl trees)
>  2. the layer tree hosts now own a list of active animation controllers. This allows for a couple of nice things
>  __a. Ticking the animation controllers no longer requires a tree walk
>  __b. We will be able to support ticking of animation controllers for layers that are not yet added to the layer tree. (Support coming in a future patch).
>  3. animation controllers register and unregister themselves from their respective layer tree host's list when they have an animation to tick.
>
> BUG=162111
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=171714

TBR=vollick@chromium.org
BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=171981