Rework how ServiceObjects are created and cached in Observatory.

runtime/bin/vmservice/client/lib/src/elements/function_ref.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 function_ref_element;
 
 import 'package:polymer/polymer.dart';
+import 'package:observatory/service.dart';
 import 'service_ref.dart';
 
 @CustomTag('function-ref')
 class FunctionRefElement extends ServiceRefElement {
   @published bool qualified = true;
 
   void refChanged(oldValue) {
     super.refChanged(oldValue);
     notifyPropertyChange(#hasParent, 0, 1);
     notifyPropertyChange(#hasClass, 0, 1);
-    hasParent = (ref != null && ref['parent'] != null);
-    hasClass = (ref != null &&
-                ref['class'] != null &&
-                ref['class']['name'] != null &&
-                ref['class']['name'] != '::');
+    ServiceMap refMap = ref;
+    hasParent = (refMap != null && refMap['parent'] != null);
+    hasClass = (refMap != null &&
+                refMap['class'] != null &&
+                refMap['class']['name'] != null &&
+                refMap['class']['name'] != '::');
   }
 
   @observable bool hasParent = false;
   @observable bool hasClass = false;
 
   FunctionRefElement.created() : super.created();
 }