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

tests/standalone/io/http_body_test.dart

Index: tests/standalone/io/http_body_test.dart
diff --git a/tests/standalone/io/http_body_test.dart b/tests/standalone/io/http_body_test.dart
index 12d819f3be32bc6abc9115c12da6da83b4d7a67e..c25406e0f643111ee6a681341000b179e94fbf88 100644
--- a/tests/standalone/io/http_body_test.dart
+++ b/tests/standalone/io/http_body_test.dart
@@ -21,7 +21,7 @@ void testHttpClientResponseBody() {
             onDone: () {
               request.response.headers.contentType =
                   new ContentType.fromString(mimeType);
-              request.response.writeBytes(content);
+              request.response.add(content);
               request.response.close();
             });
       });
@@ -118,7 +118,7 @@ void testHttpServerRequestBody() {
           .then((request) {
             request.headers.contentType =
                 new ContentType.fromString(mimeType);
-            request.writeBytes(content);
+            request.add(content);
             return request.close();
           })
           .then((response) {