Fix crash when a closure self-referenced in a try.

tests/language/closure_self_reference_test.dart

+// Copyright (c) 2014, 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';
+
+// Tests a self-reference of a closure inside a try/catch.
+// Dart2js must not try to box the closure-reference.
+
+main() {
+  var counter = 0;
+  inner(value) {
+    if (value == 0) return 0;
+    try {
+      return inner(value - 1);
+    } finally {
+      counter++;
+    }
+  }
+
+  Expect.equals(0, inner(499));
+  Expect.equals(499, counter);
+}