Don't expose mangling/minification scheme in Symbol.toString.

BUG=http://dartbug.com/9285
R=mlippautz@google.com

Review URL: https://codereview.chromium.org//385903002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@38143 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/runtime/lib/symbol_patch.dart b/runtime/lib/symbol_patch.dart
index be09eae..35a0d88 100644
--- a/runtime/lib/symbol_patch.dart
+++ b/runtime/lib/symbol_patch.dart
@@ -2,7 +2,11 @@
 // 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 'dart:mirrors';
+
 patch class Symbol {
   /* patch */ const Symbol(String name)
       : this._name = name;
+
+  /* patch */ toString() => 'Symbol("${MirrorSystem.getName(this)}")';
 }