CC Animations: Establish AnimationHost, AnimationTimeline and AnimationPlayer

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index a49873696818f5c5c6434a586166b4b92b345b1d..ded74eec294b233fbdf123ef2201ebf577eb587d 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -129,11 +129,14 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
   if (layer_tree_host_ == host)
     return;
 
-  if (layer_tree_host_)
+  if (layer_tree_host_) {
     layer_tree_host_->property_trees()->needs_rebuild = true;
-
-  if (host)
+    layer_tree_host_->UnregisterLayer(this);
+  }
+  if (host) {
     host->property_trees()->needs_rebuild = true;
+    host->RegisterLayer(this);
+  }
 
   InvalidatePropertyTreesIndices();