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

tests/language/for_test.dart

Index: tests/language/for_test.dart
diff --git a/tests/language/for_test.dart b/tests/language/for_test.dart
index 96773998d0144803d76576db0cca8ceb1a579759..a9560e910ed8fc100b8a2e0aced7235ed221a4b2 100644
--- a/tests/language/for_test.dart
+++ b/tests/language/for_test.dart
@@ -45,6 +45,13 @@ class Helper {
     }
     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 {
@@ -67,6 +74,8 @@ class ForTest {
 
     Helper.f5();
     Expect.equals(1, Helper.status);
+
+    Expect.equals(3, Helper.f6());
   }
 }