dart2dart: Fix a scoping bug in the translation of loops.

tests/language/for_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart test program for testing for statement.
 
 import "package:expect/expect.dart";
 
 class Helper {
   static int f1() {
     for (;;) return 1;
@@ skipping 27 matching lines @@
     for (var stop = false;;) {
       if (stop) {
         break;
       } else {
         stop = true;
         continue;
       }
     }
     status = 1;
   }
+
+  static int f6() {
+    // Verify that side effects in the condition are visible after the loop.
+    int i = 0;
+    for (; ++i < 3; ) {}
+    return i;
+  }
 }
 
 class ForTest {
   static testMain() {
     Expect.equals(1, Helper.f1());
     Expect.equals(0, Helper.f2(-1));
     Expect.equals(0, Helper.f2(0));
     Expect.equals(10, Helper.f2(10));
     Expect.equals(0, Helper.f3(-1));
     Expect.equals(0, Helper.f3(0));
     Expect.equals(1, Helper.f3(1));
     Expect.equals(3, Helper.f3(2));
     Expect.equals(6, Helper.f3(3));
     Expect.equals(10, Helper.f3(4));
     Expect.equals(0, Helper.f4(-1));
     Expect.equals(0, Helper.f4(0));
     Expect.equals(1, Helper.f4(1));
     Expect.equals(6, Helper.f4(6));
     Expect.equals(6, Helper.f4(10));
 
     Helper.f5();
     Expect.equals(1, Helper.status);
+
+    Expect.equals(3, Helper.f6());
   }
 }
 
 main() {
   ForTest.testMain();
 }