Add boxing for modified variables

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

Index: pkg/compiler/lib/src/js_model/js_strategy.dart
diff --git a/pkg/compiler/lib/src/js_model/js_strategy.dart b/pkg/compiler/lib/src/js_model/js_strategy.dart
index 696345f6bf7decb96692b4d8b16d3673e1418683..72763ca64717d0c18b77ab87b0970f85184e162e 100644
--- a/pkg/compiler/lib/src/js_model/js_strategy.dart
+++ b/pkg/compiler/lib/src/js_model/js_strategy.dart
@@ -413,6 +413,7 @@ class JsClosedWorld extends ClosedWorldBase with KernelClosedWorldMixin {
       MemberEntity member,
       ir.FunctionNode originalClosureFunctionNode,
       JLibrary enclosingLibrary,
+      Map<Local, JRecordField> boxedVariables,
       KernelScopeInfo info,
       ir.Location location,
       KernelToLocalsMap localsMap) {
@@ -422,6 +423,7 @@ class JsClosedWorld extends ClosedWorldBase with KernelClosedWorldMixin {
         member,
         originalClosureFunctionNode,
         enclosingLibrary,
+        boxedVariables,
         info,
         location,
         localsMap,