Add persistent handles to service protocol and Observatory UI

runtime/observatory/lib/src/app/page.dart

 // Copyright (c) 2014, 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.
 
 part of app;
 
 class IsolateNotFound implements Exception {
   String isolateId;
   IsolateNotFound(this.isolateId);
   String toString() => "IsolateNotFound: $isolateId";
@@ skipping 248 matching lines @@
     super._visit(uri);
     getIsolate(uri).then((isolate) {
       if (element != null) {
         PortsPageElement page = element;
         page.isolate = isolate;
       }
     });
   }
 }
 
+class PersistentHandlesPage extends SimplePage {
+  PersistentHandlesPage(app)
+      : super('persistent-handles', 'persistent-handles-page', app);
+
+  void _visit(Uri uri) {
+    super._visit(uri);
+    getIsolate(uri).then((isolate) {
+      if (element != null) {
+        PersistentHandlesPageElement page = element;
+        page.isolate = isolate;
+      }
+    });
+  }
+}
+
 class HeapMapPage extends SimplePage {
   HeapMapPage(app) : super('heap-map', 'heap-map', app);
 
   void _visit(Uri uri) {
     super._visit(uri);
     getIsolate(uri).then((isolate) {
       if (element != null) {
         /// Update the page.
         HeapMapElement page = element;
         page.isolate = isolate;
@@ skipping 159 matching lines @@
     assert(element != null);
   }
 
   void _visit(Uri uri) {
     assert(element != null);
     assert(canVisit(uri));
   }
 
   bool canVisit(Uri uri) => uri.path == 'timeline';
 }