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

samples/chat/chat_server_lib.dart

Index: samples/chat/chat_server_lib.dart
diff --git a/samples/chat/chat_server_lib.dart b/samples/chat/chat_server_lib.dart
index c21adfb2989ccb53bac11a3954c18877ebfe2362..4dfc49c009793543959c039d9b258ecd254e8ec7 100644
--- a/samples/chat/chat_server_lib.dart
+++ b/samples/chat/chat_server_lib.dart
@@ -317,7 +317,7 @@ class IsolatedServer {
     response.headers.set(
         "Location", "http://$_host:$_port/${redirectPath}");
     response.contentLength = _redirectPage.length;
-    response.writeBytes(_redirectPage);
+    response.add(_redirectPage);
     response.close();
   }
 
@@ -360,7 +360,7 @@ class IsolatedServer {
     response.statusCode = HttpStatus.NOT_FOUND;
     response.headers.set("Content-Type", "text/html; charset=UTF-8");
     response.contentLength = _notFoundPage.length;
-    response.writeBytes(_notFoundPage);
+    response.add(_notFoundPage);
     response.close();
   }