Fix bug in the closure methods, where iterating over the boxed variable did not return the variable…

tests/compiler/dart2js/simple_inferrer_closure_test.dart

Index: tests/compiler/dart2js/simple_inferrer_closure_test.dart
===================================================================
--- tests/compiler/dart2js/simple_inferrer_closure_test.dart	(revision 27646)
+++ tests/compiler/dart2js/simple_inferrer_closure_test.dart	(working copy)
@@ -83,6 +83,16 @@
   return a;
 }
 
+returnIntOrNull() {
+  for (var b in [42]) {
+    var bar = 42;
+    f() => bar;
+    bar = null;
+    return f();
+  }
+  return 42;
+}
+
 class A {
   foo() {
     f() => this;
@@ -99,6 +109,7 @@
   returnDyn3();
   returnInt4();
   returnNum1();
+  returnIntOrNull();
   new A().foo();
 }
 """;
@@ -120,6 +131,7 @@
     checkReturn('returnInt2', compiler.typesTask.intType);
     checkReturn('returnInt3', compiler.typesTask.intType);
     checkReturn('returnInt4', compiler.typesTask.intType);
+    checkReturn('returnIntOrNull', compiler.typesTask.intType.nullable());
 
     checkReturn('returnDyn1', compiler.typesTask.dynamicType.nonNullable());
     checkReturn('returnDyn2', compiler.typesTask.dynamicType.nonNullable());