Fix a WebSocket crash.

tests/standalone/io/web_socket_test.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "dart:async";
@@ skipping 169 matching lines @@
         webSocket.close();
       });
 
       createClient(server.port).then((webSocket) {
         webSocket.close();
       });
     });
   }
 
 
+  void testCancelThenClose() {
+    createServer().then((server) {
+      server.transform(new WebSocketTransformer()).listen((webSocket) {
+        webSocket.listen(null).cancel();
+        webSocket.close();
+        server.close();
+      });
+
+      createClient(server.port).then((webSocket) {
+        webSocket.close();
+      });
+    });
+  }
+
+  void testCloseThenCancel() {
+    createServer().then((server) {
+      server.transform(new WebSocketTransformer()).listen((webSocket) {
+        var subscription = webSocket.listen(null);
+        webSocket.close();
+        subscription.cancel();
+        server.close();
+      });
+
+      createClient(server.port).then((webSocket) {
+        webSocket.close();
+      });
+    });
+  }
+
+
   void testListenAfterClose() {
     createServer().then((server) {
       server.transform(new WebSocketTransformer()).listen((webSocket) {
         server.close();
         webSocket.close();
         Expect.throws(() => webSocket.drain());
       });
 
       createClient(server.port).then((webSocket) {
         webSocket.close();
@@ skipping 336 matching lines @@
     testRequestResponseClientCloses(2, 3002, "Got tired", 3);
     testRequestResponseServerCloses(2, null, null);
     testRequestResponseServerCloses(2, 3001, null);
     testRequestResponseServerCloses(2, 3002, "Got tired");
     testMessageLength(125);
     testMessageLength(126);
     testMessageLength(127);
     testMessageLength(65535);
     testMessageLength(65536);
     testCloseNoListen();
+    testCancelThenClose();
+    testCloseThenCancel();
     testListenAfterClose();
     testDoubleCloseClient();
     testDoubleCloseServer();
     testImmediateCloseServer();
     testImmediateCloseClient();
     testNoUpgrade();
     testUsePOST();
     testConnections(10, 3002, "Got tired");
     testIndividualUpgrade(5);
     testFromUpgradedSocket();
     testAdditionalHeaders();
     testBasicAuthentication();
   }
 }
 
 
 void initializeSSL() {
   var testPkcertDatabase = Platform.script.resolve('pkcert').toFilePath();
   SecureSocket.initialize(database: testPkcertDatabase,
                           password: "dartdart");
 }
 
 
 main() {
   new SecurityConfiguration(secure: false).runTests();
   initializeSSL();
   new SecurityConfiguration(secure: true).runTests();
 }