Implement onClosed on a socket output stream

runtime/bin/websocket_impl.dart

Index: runtime/bin/websocket_impl.dart
diff --git a/runtime/bin/websocket_impl.dart b/runtime/bin/websocket_impl.dart
index f85c2564c62119c524f73817c94a185867b7c437..a23fde4bc96c976b2dc289dd6dcaecd8e1378ca1 100644
--- a/runtime/bin/websocket_impl.dart
+++ b/runtime/bin/websocket_impl.dart
@@ -433,8 +433,8 @@ class _WebSocketConnectionBase  {
     if (_closeReceived) {
       // Close the socket when the close frame has been sent - if it
       // does not take too long.
-      _socket.close(true);
-      _socket.outputStream.onNoPendingWrites = () {
+      _socket.outputStream.close();
+      _socket.outputStream.onClosed = () {
         if (_closeTimer != null) _closeTimer.cancel();
         _socket.close();
       };