When the socket is closed, we can end up trying to send a close packet, before we get the async 'so…

sdk/lib/io/websocket_impl.dart

Index: sdk/lib/io/websocket_impl.dart
diff --git a/sdk/lib/io/websocket_impl.dart b/sdk/lib/io/websocket_impl.dart
index d7debece5fbc71636aed893b4b72dfe91d2af28a..12539d67af22e4a883efa90484782eda991beb99 100644
--- a/sdk/lib/io/websocket_impl.dart
+++ b/sdk/lib/io/websocket_impl.dart
@@ -641,7 +641,12 @@ class _WebSocketImpl extends Stream<Event> implements WebSocket {
     } else {
       opcode = _WebSocketOpcode.TEXT;
     }
-    _sendFrame(opcode, data);
+    try {
+      _sendFrame(opcode, data);
+    } catch (_) {
+      // The socket can be closed before _socket.done have a chance
+      // to complete.
+    }
   }
 
   void _sendFrame(int opcode, [List<int> data]) {