Ref count layer 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.

[email protected],[email protected]
BUG=162111


Review URL: https://chromiumcodereview.appspot.com/11598005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@174043 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/cc/layer_tree_impl.cc b/cc/layer_tree_impl.cc
index 0c68bb9a..8d7e722 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -160,5 +160,8 @@
   return layer_tree_host_impl_->debugRectHistory();
 }
 
+AnimationRegistrar* LayerTreeImpl::animationRegistrar() const {
+  return layer_tree_host_impl_->animationRegistrar();
+}
 
 } // namespace cc