Parameterize TypeSystem by its node kind

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

Index: pkg/compiler/lib/src/types/container_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/container_type_mask.dart b/pkg/compiler/lib/src/types/container_type_mask.dart
index bbdfe1a221e5e2b0c81174100ab32a37515531f4..2bda88907736eaf478f0ccf85e30c56ee99394cc 100644
--- a/pkg/compiler/lib/src/types/container_type_mask.dart
+++ b/pkg/compiler/lib/src/types/container_type_mask.dart
@@ -7,11 +7,11 @@ part of masks;
 /// A [ContainerTypeMask] is a [TypeMask] for a specific allocation
 /// site of a container (currently only List) that will get specialized
 /// once the [TypeGraphInferrer] phase finds an element type for it.
-class ContainerTypeMask extends ForwardingTypeMask {
+class ContainerTypeMask<T> extends ForwardingTypeMask {
   final TypeMask forwardTo;
 
   // The [Node] where this type mask was created.
-  final Node allocationNode;
+  final T allocationNode;
 
   // The [Entity] where this type mask was created.
   final MemberEntity allocationElement;