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

tests/standalone/io/process_std_io_script.dart

Index: tests/standalone/io/process_std_io_script.dart
diff --git a/tests/standalone/io/process_std_io_script.dart b/tests/standalone/io/process_std_io_script.dart
index 4ca28f40f73c74e128372f2f6f400c16a2f38af5..7e55c8d85351b7d56770cb7d95728f65cff3400b 100644
--- a/tests/standalone/io/process_std_io_script.dart
+++ b/tests/standalone/io/process_std_io_script.dart
@@ -15,8 +15,8 @@ main() {
       stdin.pipe(stderr);
     } else if (options.arguments[0] == "2") {
       stdin.listen((data) {
-        stdout.writeBytes(data);
-        stderr.writeBytes(data);
+        stdout.add(data);
+        stderr.add(data);
       });
     }
   }