Very simple version of Isolates.

utils/testrunner/testrunner.dart

Index: utils/testrunner/testrunner.dart
diff --git a/utils/testrunner/testrunner.dart b/utils/testrunner/testrunner.dart
index 7ecf8ac985d5c0b833bb9df73365db95f67582ed..bd718309a6c0f36154bc4181c3c3e82bc476f654 100755
--- a/utils/testrunner/testrunner.dart
+++ b/utils/testrunner/testrunner.dart
@@ -256,8 +256,10 @@ void spawnTasks(Map config, List testFiles) {
         // We could later print a summary report here.
       }
     });
-    SendPort s = spawnUri(config['pipeline']);
-
+    var response = new ReceivePort();
+    spawnUri(config['pipeline'], response)
+        .then((_) => return response.first)
+        .then((s) {
     // Get the names of the source and target test files and containing
     // directories.
     var testPath = new Path(testfile);
@@ -280,14 +282,14 @@ void spawnTasks(Map config, List testFiles) {
       _testDir = targetDir;
     }
     if (f == null) {
-      s.send(config, port.toSendPort());
+      s.send([config, port.sendPort]);
     } else {
       f.then((_) {
-        s.send(config, port.toSendPort());
+        s.send([config, port.sendPort]);
       });
       break; // Don't do any more until pub is done.
     }
-  }
+  });
 }
 
 /**