Give instances their own model class; move DartErrors out of instance-ref into their own error-ref.

runtime/bin/vmservice/observatory/lib/src/elements/instance_view.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.
 
 library instance_view_element;
 
 import 'dart:async';
 import 'observatory_element.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('instance-view')
 class InstanceViewElement extends ObservatoryElement {
-  @published ServiceMap instance;
+  @published Instance instance;
   @published ServiceMap path;
   @published ServiceMap inboundReferences;
   @observable int retainedBytes = null;
 
   InstanceViewElement.created() : super.created();
 
   Future<ServiceObject> eval(String text) {
     return instance.isolate.get(
         instance.id + "/eval?expr=${Uri.encodeComponent(text)}");
   }
@@ skipping 17 matching lines @@
     return instance.isolate.get(instance.id + "/inbound_references?limit=$arg")
         .then((ServiceObject obj) {
            inboundReferences = obj;
         });
   }
 
   void refresh(var done) {
     instance.reload().whenComplete(done);
   }
 }