Don't call accept the c socket, if we're currently closing.

runtime/bin/socket_patch.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 patch class RawServerSocket  {
   /* patch */ static Future<RawServerSocket> bind(address,
                                                   int port,
                                                   {int backlog: 0,
                                                    bool v6Only: false}) {
     return _RawServerSocket.bind(address, port, backlog, v6Only);
@@ skipping 408 matching lines @@
     var result =
         nativeWrite(bufferAndStart.buffer, bufferAndStart.start, bytes);
     if (result is OSError) {
       reportError(result, "Write failed");
       result = 0;
     }
     return result;
   }
 
   _NativeSocket accept() {
+    // Don't issue accept if we're closing.
+    if (isClosing || isClosed) return null;
     var socket = new _NativeSocket.normal();
     if (nativeAccept(socket) != true) return null;
     socket.localPort = localPort;
     socket.address = address;
     return socket;
   }
 
   int get port {
     if (localPort != null) return localPort;
     return localPort = nativeGetPort();
@@ skipping 777 matching lines @@
     if (_detachReady != null) {
       _detachReady.complete(null);
     } else {
       if (_raw != null) {
         _raw.shutdown(SocketDirection.SEND);
         _disableWriteEvent();
       }
     }
   }
 }