Further cleanup of element use in type_graph_nodes

pkg/compiler/lib/src/types/map_type_mask.dart

Index: pkg/compiler/lib/src/types/map_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/map_type_mask.dart b/pkg/compiler/lib/src/types/map_type_mask.dart
index 4fe6a79393d810e5de3830916bcb65f386923f3c..5152b9d217b3fa942405d549f6702fd9d3f67e07 100644
--- a/pkg/compiler/lib/src/types/map_type_mask.dart
+++ b/pkg/compiler/lib/src/types/map_type_mask.dart
@@ -15,8 +15,8 @@ class MapTypeMask extends ForwardingTypeMask {
   // The [Node] where this type mask was created.
   final Node allocationNode;
 
-  // The [Entity] where this type mask was created.
-  final Entity allocationElement;
+  // The [MemberEntity] where this type mask was created.
+  final MemberEntity allocationElement;
 
   // The value type of this map.
   final TypeMask valueType;