cc: Use Element Id to Record Animation Changes

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index feca5e7a1343d905641653c39382dc2c3191cf79..d34a1998f2ffed02ddb50639c0ed2875177c283a 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -516,9 +516,12 @@ class CC_EXPORT LayerTreeImpl {
 
   std::unordered_map<ElementId, int, ElementIdHash> element_layers_map_;
 
-  std::unordered_map<int, float> opacity_animations_map_;
-  std::unordered_map<int, gfx::Transform> transform_animations_map_;
-  std::unordered_map<int, FilterOperations> filter_animations_map_;
+  std::unordered_map<ElementId, float, ElementIdHash>
+      element_id_to_opacity_animations_;
+  std::unordered_map<ElementId, gfx::Transform, ElementIdHash>
+      element_id_to_transform_animations_;
+  std::unordered_map<ElementId, FilterOperations, ElementIdHash>
+      element_id_to_filter_animations_;
 
   // Maps from clip layer ids to scroll layer ids.  Note that this only includes
   // the subset of clip layers that act as scrolling containers.  (This is