Register created closure class with the world.

pkg/compiler/lib/src/js_model/closure_visitors.dart

Index: pkg/compiler/lib/src/js_model/closure_visitors.dart
diff --git a/pkg/compiler/lib/src/js_model/closure_visitors.dart b/pkg/compiler/lib/src/js_model/closure_visitors.dart
index 1d4a6e2ce9bca2166690a781ff49a4aa49ec6491..1dcb29f8de16034239276ab4e1abeaba32bf6eaa 100644
--- a/pkg/compiler/lib/src/js_model/closure_visitors.dart
+++ b/pkg/compiler/lib/src/js_model/closure_visitors.dart
@@ -22,8 +22,8 @@ class ClosureScopeBuilder extends ir.Visitor {
   /// A map of the nodes that we have flagged as necessary to generate closure
   /// classes for in a later stage. We map that node to information ascertained
   /// about variable usage in the surrounding scope.
-  Map<ir.Node /* ir.Field | ir.FunctionNode */, ScopeInfo> _closuresToGenerate =
-      <ir.Node, ScopeInfo>{};
+  Map<ir.TreeNode /* ir.Field | ir.FunctionNode */, ScopeInfo>
+      _closuresToGenerate = <ir.TreeNode, ScopeInfo>{};
 
   /// The local variables that have been declared in the current scope.
   List<ir.VariableDeclaration> _scopeVariables;