Add boxing for modified variables

pkg/compiler/lib/src/ssa/locals_handler.dart

Index: pkg/compiler/lib/src/ssa/locals_handler.dart
diff --git a/pkg/compiler/lib/src/ssa/locals_handler.dart b/pkg/compiler/lib/src/ssa/locals_handler.dart
index 363511b1d4f915fcf257614e8481bead87a3a3cd..60aa04ea7deab717bc7426a8397bcac333d941b6 100644
--- a/pkg/compiler/lib/src/ssa/locals_handler.dart
+++ b/pkg/compiler/lib/src/ssa/locals_handler.dart
@@ -155,9 +155,7 @@ class LocalsHandler {
     directLocals[closureInfo.context] = box;
     // Make sure that accesses to the boxed locals go into the box. We also
     // need to make sure that parameters are copied into the box if necessary.
-    closureInfo.forEachBoxedVariable((_from, _to) {
-      LocalVariableElement from = _from;
-      BoxFieldElement to = _to;
+    closureInfo.forEachBoxedVariable((Local from, FieldEntity to) {
       // The [from] can only be a parameter for function-scopes and not
       // loop scopes.
       if (from.isRegularParameter && !forGenerativeConstructorBody) {