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

tests/standalone/io/http_shutdown_test.dart

Index: tests/standalone/io/http_shutdown_test.dart
diff --git a/tests/standalone/io/http_shutdown_test.dart b/tests/standalone/io/http_shutdown_test.dart
index 18060c8026849e7ec3560f030ed7f13db3db3220..1cf48032f6c2450299852b789b8a7187ae1afee7 100644
--- a/tests/standalone/io/http_shutdown_test.dart
+++ b/tests/standalone/io/http_shutdown_test.dart
@@ -165,7 +165,7 @@ void test5(int totalConnections) {
     for (int i = 0; i < totalConnections; i++) {
       client.post("127.0.0.1", server.port, "/")
         .then((request) {
-            request.writeBytes([0]);
+            request.add([0]);
             // TODO(sgjesse): Make this test work with
             //request.response instead of request.close() return
             //return request.response;