Fix issue 22875

tests/language/await_postfix_expr_test.dart

 // Copyright (c) 2015, 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 "dart:async";
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 
 
 post0(a) async {
@@ skipping 13 matching lines @@
 }
 
 sum(a) async {
   var s = 0;
   for (int i = 0; i < a.length; /* nothing */) {
     s += a[await i++];
   }
   return s;
 }
 
+// Adapted from repro case for issue 22875.
+sum2(n) async {
+  int i, s = 0;
+  for (i = 1; i <= n; await i++) {
+    // The loop-local variable j was necessary for the crash in 22785.
+    var j = await i;
+    s += j;
+  }
+  return s;
+}
+
 test() async {
   Expect.equals(10, await post0(10));
   Expect.equals(21, await post1(10));
   Expect.equals(11, await pref0(10));
   Expect.equals(23, await pref1(10));
   Expect.equals(10, await sum([1, 2, 3, 4]));
+  Expect.equals(10, await sum2(4));
 }
 
 main() {
   asyncStart();
   test().then((_) {
     asyncEnd();
   });
 }