Rework how ServiceObjects are created and cached in Observatory.

runtime/bin/vmservice/client/lib/src/elements/isolate_profile.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 isolate_profile_element;
 
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:logging/logging.dart';
 import 'package:observatory/service.dart';
@@ skipping 59 matching lines @@
     return '${percent.toStringAsFixed(2)}%';
   }
 
   ProfileCallerTreeRow(this.profile, this.code, ProfileCallerTreeRow parent) :
       super(parent) {
     assert(profile != null);
     assert(code != null);
     var totalSamples = profile['samples'];
     // When the row is created, fill out the columns.
     if (parent == null) {
-      var root = profile.isolate.codes.tagRoot();
+      var root = profile.isolate.tagRoot();
       var totalAttributedCalls = root.callersCount(code);
       var totalParentCalls = root.sumCallersCount();
       columns.add(formatPercent(totalAttributedCalls, totalParentCalls));
     } else {
       var totalAttributedCalls = parent.code.callersCount(code);
       var totalParentCalls = parent.code.sumCallersCount();
       columns.add(formatPercent(totalAttributedCalls, totalParentCalls));
     }
     columns.add(formatPercent(code.exclusiveTicks, totalSamples));
   }
@@ skipping 90 matching lines @@
 
   void _update() {
     if (profile == null) {
       return;
     }
     _buildTree();
   }
 
   void _buildCallersTree() {
     assert(profile != null);
-    var root = profile.isolate.codes.tagRoot();
+    var root = profile.isolate.tagRoot();
     if (root == null) {
       Logger.root.warning('No profile root tag.');
     }
     try {
       tree.initialize(new ProfileCallerTreeRow(profile, root, null));
     } catch (e, stackTrace) {
       Logger.root.warning('_buildCallersTree', e, stackTrace);
     }
 
     notifyPropertyChange(#tree, null, tree);
@@ skipping 33 matching lines @@
 
   @observable void toggleExpanded(Event e, var detail, Element target) {
     var row = target.parent;
     if (row is TableRowElement) {
       // Subtract 1 to get 0 based indexing.
       tree.toggle(row.rowIndex - 1);
     }
   }
 
 }