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 19b505b49618f20930f7d55212eb63f072d5349a..80a21cee5656d9bdc0ba6334ddb8b7fa5f7c8ea3 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -116,7 +116,11 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
   if (layer_tree_host_ == host)
     return;
 
+  if (layer_tree_host_)
+    layer_tree_host_->UnregisterLayer(this);
   layer_tree_host_ = host;
+  if (layer_tree_host_)
+    layer_tree_host_->RegisterLayer(this);
 
   // When changing hosts, the layer needs to commit its properties to the impl
   // side for the new host.