Migrate block 115.

tests/language_2/gvn_interceptor_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 
 foo(a, index) {
   if (a.length < index) {
     for (int i = a.length; i <= index; i++) a.add(i);
   }
   // dart2js was reusing the a.length from above.
   return a[a.length - 1];
 }
 
 void main() {
   Expect.equals(3, foo([0], 3));
 }