Fix bug where a parameter was mutated while it was still used.

tests/language/src/LivenessTest.dart

Index: tests/language/src/LivenessTest.dart
diff --git a/tests/language/src/LivenessTest.dart b/tests/language/src/LivenessTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..08d84e7357ebb8539371638b34180e47f2cf5021
--- /dev/null
+++ b/tests/language/src/LivenessTest.dart
@@ -0,0 +1,14 @@
+// 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.
+// Dart test program testing closures.
+
+foo(x) {
+  var y = x;
+  for (int i = 0; i < 10; i++) x++;
+  return y;
+}
+
+main() {
+  Expect.equals(499, foo(499));
+}