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

tests/standalone/io/http_client_connect_test.dart

Index: tests/standalone/io/http_client_connect_test.dart
diff --git a/tests/standalone/io/http_client_connect_test.dart b/tests/standalone/io/http_client_connect_test.dart
index 69acd441d76303c4f96cfc5344a8571e70e99650..9c18e75d9b1553f7a594a171271a84126c4596ee 100644
--- a/tests/standalone/io/http_client_connect_test.dart
+++ b/tests/standalone/io/http_client_connect_test.dart
@@ -33,7 +33,7 @@ void testGetDataRequest() {
   HttpServer.bind().then((server) {
     var data = "lalala".codeUnits;
     server.listen((request) {
-      request.response.writeBytes(data);
+      request.response.add(data);
       request.pipe(request.response);
     });