Revert of Use element id's for animations

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 1e72ae407068f493d0ea265197f93cbe9be2712d..7195f56f06b724ff8d9fe702b8b49d184aa87752 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -347,10 +347,6 @@
   void SetLayerTreeMutator(std::unique_ptr<LayerTreeMutator> mutator);
 
   Layer* LayerById(int id) const;
-
-  Layer* LayerByElementId(ElementId element_id) const;
-  void AddToElementMap(Layer* layer);
-  void RemoveFromElementMap(Layer* layer);
 
   void AddLayerShouldPushProperties(Layer* layer);
   void RemoveLayerShouldPushProperties(Layer* layer);
@@ -425,8 +421,6 @@
   bool IsRemoteClient() const;
   void BuildPropertyTreesForTesting();
 
-  void SetElementIdsForTesting();
-
   ImageSerializationProcessor* image_serialization_processor() const {
     return image_serialization_processor_;
   }
@@ -597,10 +591,6 @@
 
   using LayerIdMap = std::unordered_map<int, Layer*>;
   LayerIdMap layer_id_map_;
-
-  using ElementLayersMap = std::unordered_map<ElementId, Layer*, ElementIdHash>;
-  ElementLayersMap element_layers_map_;
-
   // Set of layers that need to push properties.
   std::unordered_set<Layer*> layers_that_should_push_properties_;