Add persistent handles to service protocol and Observatory UI

runtime/observatory/observatory_sources.gypi

 # Copyright (c) 2015, 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.
 
 # This file contains all dart, css, and html sources for Observatory.
 {
   'sources': [
     'lib/app.dart',
     'lib/cli.dart',
     'lib/cpu_profile.dart',
@@ skipping 101 matching lines @@
     'lib/src/elements/object_common.dart',
     'lib/src/elements/object_common.html',
     'lib/src/elements/object_view.dart',
     'lib/src/elements/object_view.html',
     'lib/src/elements/objectpool_view.dart',
     'lib/src/elements/objectpool_view.html',
     'lib/src/elements/observatory_application.dart',
     'lib/src/elements/observatory_application.html',
     'lib/src/elements/observatory_element.dart',
     'lib/src/elements/observatory_element.html',
+    'lib/src/elements/persistent_handles.dart',
+    'lib/src/elements/persistent_handles.html',
     'lib/src/elements/ports.dart',
     'lib/src/elements/ports.html',
     'lib/src/elements/script_inset.dart',
     'lib/src/elements/script_inset.html',
     'lib/src/elements/script_ref.dart',
     'lib/src/elements/script_ref.html',
     'lib/src/elements/script_view.dart',
     'lib/src/elements/script_view.html',
     'lib/src/elements/service_ref.dart',
     'lib/src/elements/service_ref.html',
@@ skipping 19 matching lines @@
     'lib/tracer.dart',
     'lib/utils.dart',
     'web/index.html',
     'web/main.dart',
     'web/favicon.ico',
     'web/third_party/trace_viewer_full.html',
     'web/timeline.js',
     'web/timeline.html',
   ],
 }