Reapply "Added for-loop variable tracking and regular closures/initializers captured variable track…

tests/compiler/dart2js/forloop_box_test.dart

Index: tests/compiler/dart2js/forloop_box_test.dart
diff --git a/tests/compiler/dart2js/forloop_box_test.dart b/tests/compiler/dart2js/forloop_box_test.dart
index e44bf61c537ebb6861dc53ea2b9e8aaef2fa59f1..f27995f89874dd8cfa87aa2925f2a9c1e49084da 100644
--- a/tests/compiler/dart2js/forloop_box_test.dart
+++ b/tests/compiler/dart2js/forloop_box_test.dart
@@ -6,7 +6,7 @@ import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'compiler_helper.dart';
 
-String TEST = r'''
+String SHOULD_NOT_BE_BOXED_TEST = r'''
 main() {
   var a;
   for (var i=0; i<10; i++) {
@@ -16,7 +16,7 @@ main() {
 }
 ''';
 
-String NEGATIVE_TEST = r'''
+String SHOULD_BE_BOXED_TEST = r'''
 run(f) => f();
 main() {
   var a;
@@ -27,13 +27,31 @@ main() {
 }
 ''';
 
+String ONLY_UPDATE_LOOP_VAR_TEST = r'''
+run(f) => f();
 main() {
-  asyncTest(() => compileAll(TEST).then((generated) {
+  var a;
+  for (var i=0; i<10; run(() => i++)) {
+    var b = 3;
+    a = () => b = i;
+  }
+  print(a());
+}
+''';
+
+main() {
+  asyncTest(() => compileAll(SHOULD_NOT_BE_BOXED_TEST).then((generated) {
         Expect.isTrue(generated.contains('main_closure(i)'),
-            'for-loop variable was boxed');
+            'for-loop variable should not have been boxed');
+      }));
+  asyncTest(() => compileAll(SHOULD_BE_BOXED_TEST).then((generated) {
+        Expect.isFalse(generated.contains('main_closure(i)'),
+            'for-loop variable should have been boxed');
       }));
-  asyncTest(() => compileAll(NEGATIVE_TEST).then((generated) {
+  asyncTest(() => compileAll(ONLY_UPDATE_LOOP_VAR_TEST).then((generated) {
         Expect.isFalse(generated.contains('main_closure(i)'),
-            'for-loop variable was not boxed');
+            'for-loop variable should have been boxed');
+        Expect.isFalse(generated.contains(', _box_0.b = 3,'),
+            'non for-loop captured variable should not be updated in loop');
       }));
 }