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

tests/standalone/io/raw_secure_socket_pause_test.dart

Index: tests/standalone/io/raw_secure_socket_pause_test.dart
diff --git a/tests/standalone/io/raw_secure_socket_pause_test.dart b/tests/standalone/io/raw_secure_socket_pause_test.dart
index 906ef4ebbecb3150ec1ea9c1570b28c4148ad56e..d70311299f264402bb8c79088614b651912e8b06 100644
--- a/tests/standalone/io/raw_secure_socket_pause_test.dart
+++ b/tests/standalone/io/raw_secure_socket_pause_test.dart
@@ -24,7 +24,7 @@ Future<HttpServer> startServer() {
         onDone: () {
           request.response.contentLength = 100;
           for (int i = 0; i < 10; i++) {
-            request.response.writeBytes([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+            request.response.add([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
           }
           request.response.close();
         });