Remove StreamSink(replaced by EventSink) and make IOSink extend EventSink.

tests/standalone/io/socket_invalid_arguments_test.dart

Index: tests/standalone/io/socket_invalid_arguments_test.dart
diff --git a/tests/standalone/io/socket_invalid_arguments_test.dart b/tests/standalone/io/socket_invalid_arguments_test.dart
index 9a49a729f0050ce15afd9d5ac8daa6dd62b0cda1..61d526db60924c0b00df2dff2f266aaec1759c4d 100644
--- a/tests/standalone/io/socket_invalid_arguments_test.dart
+++ b/tests/standalone/io/socket_invalid_arguments_test.dart
@@ -40,7 +40,7 @@ testAdd(buffer) {
             socket.destroy();
             server.close();
           });
-      socket.writeBytes(buffer);
+      socket.add(buffer);
     });
   });
 }