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

tests/standalone/io/dart_std_io_pipe_script.dart

Index: tests/standalone/io/dart_std_io_pipe_script.dart
diff --git a/tests/standalone/io/dart_std_io_pipe_script.dart b/tests/standalone/io/dart_std_io_pipe_script.dart
index 1299645c6a7d982e0129067e08f81d7ac034b003..76402d65c605c9c9f853a5e1bd1edb6169c75e3b 100644
--- a/tests/standalone/io/dart_std_io_pipe_script.dart
+++ b/tests/standalone/io/dart_std_io_pipe_script.dart
@@ -27,8 +27,8 @@ 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);
       });
     }
   }