Don’t call toString from debugger

tests/standalone/debugger/tostring_throws_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 "debug_lib.dart";
 
 main(List<String> arguments) {
   if (RunScript(testScript, arguments)) return;
 
   Foo foo = new Foo();
 
   print("Hello from debuggee");
 }
 
 class Foo {
   String toString() {
     throw 'I always throw';
   }
 }
 
+// Make sure Foo.toString() does not get called.
 var testScript = [
   MatchFrame(0, "main"),
   SetBreakpoint(12),
   Resume(),
   MatchFrame(0, "main"),
-  MatchLocals({"foo": "#ERROR"}),
+  MatchLocals({"foo": "object of type Foo"}),
   Resume(),
 ];