[turbofan] Fix context chain extension for top-level code.

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index 6d14c75d7801be922dfdcf2c71b440d9229eddf3..42fa53f6c7c9e055e9650b01b4db84ca7f68fb7c 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -145,6 +145,7 @@ class AstGraphBuilder : public AstVisitor {
   void CreateFunctionContext(bool constant_context);
 
   // Get or create the node that represents the outer function closure.
+  Node* GetFunctionClosureForContext();
   Node* GetFunctionClosure();
 
   // Node creation helpers.