Add a ListOutputStream.onData callback.

tests/standalone/io/list_input_stream_test.dart

Index: tests/standalone/io/list_input_stream_test.dart
diff --git a/tests/standalone/io/list_input_stream_test.dart b/tests/standalone/io/list_input_stream_test.dart
index b4aa435c6884c14813ef95e603159ef4c209cd53..08e2ea00508ea58a8ad72db9eed3ccc5dff6b268 100644
--- a/tests/standalone/io/list_input_stream_test.dart
+++ b/tests/standalone/io/list_input_stream_test.dart
@@ -105,7 +105,7 @@ void testListInputStreamPipe1() {
   ReceivePort donePort = new ReceivePort();
 
   void onClosed() {
-    var contents = output.contents();
+    var contents = output.read();
     Expect.equals(data.length, contents.length);
     donePort.toSendPort().send(null);
   }
@@ -135,7 +135,7 @@ void testListInputStreamPipe2() {
       }
       count++;
     } else {
-      var contents = output.contents();
+      var contents = output.read();
       Expect.equals(data.length * 10, contents.length);
       donePort.toSendPort().send(null);
     }