Add persistent handles to service protocol and Observatory UI

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

Index: runtime/observatory/lib/src/app/page.dart
diff --git a/runtime/observatory/lib/src/app/page.dart b/runtime/observatory/lib/src/app/page.dart
index 6be5e884a099af6a7761ebbdd56520f2398f0cb7..b2216e40b4d420d62ed2dcfbfff47345299e3d41 100644
--- a/runtime/observatory/lib/src/app/page.dart
+++ b/runtime/observatory/lib/src/app/page.dart
@@ -266,6 +266,21 @@ class PortsPage extends SimplePage {
   }
 }
 
+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);