Record names of constructors and use that to implement Object.toString.

dart/frog/tests/leg_only/src/ToStringTest.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.
+
+class A extends Object {
+}
+
+main() {
+  Expect.equals("[Instance of 'Object']", new Object().toString());
+  Expect.equals("[Instance of 'A']", new A().toString());

[Lasse Reichstein, 2012/01/11 09:49:16]

If List.toString should return "Instance of 'List'", then test that here too,
just for good measure (even though it goes through the interceptor).

+}