Dart: Futures -> Callbacks.

benchmarks/mojo_rtt_benchmark/lib/echo_server.dart

Index: benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
diff --git a/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart b/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
index 04a2601582778318673e3220707f38d322c0b3a9..dbb6295494bfe2b740cf513921d7b298019034e7 100644
--- a/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
+++ b/benchmarks/mojo_rtt_benchmark/lib/echo_server.dart
@@ -18,8 +18,9 @@ class EchoImpl implements Echo {
     _echo.ctrl.onError = _errorHandler;
   }
 
-  echoString(String value, [Function responseFactory]) =>
-      responseFactory(value);
+  void echoString(String value, void respond(String response)) {
+    respond(value);
+  }
 
   Future close() => _echo.close();