CC Animation: Use ElementId to attach CC animation players.

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index fb445ecc84b66e2f0289b496cb0b10526717faf6..84ced559d970284fba8730f88b5d8ea30f9e0c96 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -122,10 +122,14 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
   if (layer_tree_host_) {
     layer_tree_host_->property_trees()->needs_rebuild = true;
     layer_tree_host_->UnregisterLayer(this);
+    if (element_id())
+      layer_tree_host_->UnregisterLayerForElementId(this);
   }
   if (host) {
     host->property_trees()->needs_rebuild = true;
     host->RegisterLayer(this);
+    if (element_id())
+      host->RegisterLayerForElementId(this);
   }
 
   layer_tree_host_ = host;
@@ -843,7 +847,15 @@ void Layer::SetScrollClipLayerId(int clip_layer_id) {
   DCHECK(IsPropertyChangeAllowed());
   if (scroll_clip_layer_id_ == clip_layer_id)
     return;
+
+  if (layer_tree_host_ && element_id())
+    layer_tree_host_->UnregisterLayerForElementId(this);
+
   scroll_clip_layer_id_ = clip_layer_id;
+
+  if (layer_tree_host_ && element_id())
+    layer_tree_host_->RegisterLayerForElementId(this);
+
   SetNeedsCommit();
 }
 
@@ -1731,7 +1743,14 @@ void Layer::SetElementId(ElementId id) {
     return;
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
                "Layer::SetElementId", "id", id);
+  if (layer_tree_host_ && element_id())
+    layer_tree_host_->UnregisterLayerForElementId(this);
+
   element_id_ = id;
+
+  if (layer_tree_host_ && element_id())
+    layer_tree_host_->RegisterLayerForElementId(this);
+
   SetNeedsCommit();
 }