Fix several bugs in closure conversion.

pkg/kernel/testcases/closures/for_in_closure.dart

 // Copyright (c) 2016, 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.md file.
 
 const numbers = const <int>[0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
 
 main() {
   var closures = [];
+  var captured_outside = 0;
   for (int i in numbers) {
-    closures.add(() => i);
+    closures.add(() => i + captured_outside);
   }
   int sum = 0;
   for (Function f in closures) {
     sum += f();
   }
   // This formula is credited to Gauss. Search for "Gauss adding 1 to 100".
   int expectedSum = (numbers.length - 1) * numbers.length ~/ 2;
   if (expectedSum != sum) {
     throw new Exception("Unexpected sum = $sum != $expectedSum");
   }
 }