Ensure stack trace are identical.

dart/tests/language/identical_trace_test.dart

+// Copyright (c) 2013, 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';
+
+main() {
+  var st1;
+  try {
+    try {
+      throw 'bad';
+    } catch (e, st) {
+      st1 = st;
+      rethrow;
+    }
+    Expect.fail('Exception expected');
+  } catch (e, st2) {
+    Expect.equals(st1, st2);
+    Expect.identical(st1, st2);
+    return;
+  }
+  Expect.fail('Exception expected');
+}