Fixes #254 - Better stacktrace support

lib/runtime/dart_library.js

 // Copyright (c) 2015, 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.
 
 /* This file defines the module loader for the dart runtime.
 */
 
 var dart_library;
 (function (dart_library) {
   'use strict';
@@ skipping 101 matching lines @@
     let _isolate_helper = import_('dart/_isolate_helper');
     _isolate_helper.startRootIsolate(library.main, []);
   }
   dart_library.start = start;
 
   let _bootstrapped = false;
   function bootstrap() {
     if (_bootstrapped) return;
     _bootstrapped = true;
 
-   // Force import of core.
-    import_('dart/core');
+    // Force import of core.
+    var core = import_('dart/core');
+    core.Object.toString = function() {
+      // Interface types are represented by the corresponding constructor
+      // function.  This ensures that Dart interface types print properly.
+      return this.name;
+    }
 
     // TODO(vsm): DOM facades?
     // See: https://github.com/dart-lang/dev_compiler/issues/173
     NodeList.prototype.get = function(i) { return this[i]; };
     NamedNodeMap.prototype.get = function(i) { return this[i]; };
     DOMTokenList.prototype.get = function(i) { return this[i]; };
     HTMLCollection.prototype.get = function(i) { return this[i]; };
 
   }
 
 })(dart_library || (dart_library = {}));