Dart: Futures -> Callbacks.

mojo/dart/apptests/test_apps/echo/lib/main.dart

Index: mojo/dart/apptests/test_apps/echo/lib/main.dart
diff --git a/mojo/dart/apptests/test_apps/echo/lib/main.dart b/mojo/dart/apptests/test_apps/echo/lib/main.dart
index 4a203b9501f14cbb783c585225e28562f4182a51..45040a9758499bc3a543e3273b0ddfebcea01b6d 100644
--- a/mojo/dart/apptests/test_apps/echo/lib/main.dart
+++ b/mojo/dart/apptests/test_apps/echo/lib/main.dart
@@ -17,20 +17,20 @@ class EchoServiceImpl implements EchoService {
     _service = new EchoServiceInterface.fromEndpoint(endpoint, this);
   }
 
-  dynamic echoString(String value, [Function responseFactory]) {
+  void echoString(String value, void callback(String value)) {
     if (value == "quit") {
       _service.close();
     }
-    return responseFactory(value);
+    callback(value);
   }
 
-  dynamic delayedEchoString(String value, int millis,
-      [Function responseFactory]) {
+  void delayedEchoString(
+      String value, int millis, void callback(String value)) {
     if (value == "quit") {
       _service.close();
     }
-    return new Future.delayed(
-        new Duration(milliseconds: millis), () => responseFactory(value));
+    new Future.delayed(
+        new Duration(milliseconds: millis), () => callback(value));
   }
 
   void swap() {