Add Observatory mojo_shell hearbeat test

sky/engine/core/script/dart_service_isolate/server.dart

Index: sky/engine/core/script/dart_service_isolate/server.dart
diff --git a/sky/engine/core/script/dart_service_isolate/server.dart b/sky/engine/core/script/dart_service_isolate/server.dart
index f0d5f86f908de919bdd807dfd8ed08d4c5e2ce8c..7fa478876e68e2eff00b2147c267e1168cd3c21a 100644
--- a/sky/engine/core/script/dart_service_isolate/server.dart
+++ b/sky/engine/core/script/dart_service_isolate/server.dart
@@ -151,8 +151,8 @@ class Server {
       request.response.close();
       return;
     }
-    var message = new Message.fromUri(this, request.uri);
     var client = new HttpRequestClient(request, _service);
+    var message = new Message.fromUri(client, request.uri);
     client.onMessage(null, message);
   }