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

tests/language/while_test.dart

Index: tests/language/while_test.dart
diff --git a/tests/language/while_test.dart b/tests/language/while_test.dart
index 5263d755dc6f79c1c6aa2e959a6290b5957bcefe..71f3c5d0ba7326273c84cf5e0200831150ae0cc6 100644
--- a/tests/language/while_test.dart
+++ b/tests/language/while_test.dart
@@ -27,6 +27,13 @@ class Helper {
     }
     return i;
   }
+
+  static int f4() {
+    // Verify that side effects in the condition are visible after the loop.
+    int i = 0;
+    while (++i < 3) {}
+    return i;
+  }
 }
 
 class WhileTest {
@@ -40,6 +47,7 @@ class WhileTest {
     Expect.equals(0, Helper.f3(0));
     Expect.equals(1, Helper.f3(1));
     Expect.equals(2, Helper.f3(2));
+    Expect.equals(3, Helper.f4());
   }
 }