Don't throw exceptions when adding to a IOSink(StreamSink) after close.

tests/standalone/io/socket_upgrade_to_secure_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 "package:expect/expect.dart";
@@ skipping 142 matching lines @@
   Future<SecureSocket> connectClient(int port) {
     if (!handshakeBeforeSecure) {
       return Socket.connect(HOST_NAME, port).then((socket) {
         var future;
         if (hostnameInConnect) {
           future = SecureSocket.secure(socket);
         } else {
           future = SecureSocket.secure(socket, host: HOST_NAME);
         }
         return future.then((secureSocket) {
-          Expect.throws(() => socket.add([0]));
+          socket.add([0]);
           return secureSocket;
         });
       });
     } else {
       return Socket.connect(HOST_NAME, port).then((socket) {
         return runClientHandshake(socket).then((_) {
             var future;
             if (hostnameInConnect) {
               future = SecureSocket.secure(socket);
             } else {
               future = SecureSocket.secure(socket, host: HOST_NAME);
             }
             return future.then((secureSocket) {
-              Expect.throws(() => socket.add([0]));
+              socket.add([0]);
               return secureSocket;
             });
         });
       });
     }
   }
 
   serverReady(server) {
     server.listen((client) {
       if (!handshakeBeforeSecure) {
         SecureSocket.secureServer(client, CERTIFICATE).then((secureClient) {
-          Expect.throws(() => client.add([0]));
+          client.add([0]);
           runServer(secureClient).then((_) => server.close());
         });
       } else {
         runServerHandshake(client).then((carryOverData) {
           SecureSocket.secureServer(
               client,
               CERTIFICATE,
               bufferedData: carryOverData).then((secureClient) {
-            Expect.throws(() => client.add([0]));
+            client.add([0]);
             runServer(secureClient).then((_) => server.close());
           });
         });
       }
     });
 
     connectClient(server.port).then(runClient).then((socket) {
       port.close();
     });
   }
 
   ServerSocket.bind(HOST_NAME, 0).then(serverReady);
 }
 
 main() {
   Path scriptDir = new Path(Platform.script).directoryPath;
   Path certificateDatabase = scriptDir.append('pkcert');
   SecureSocket.initialize(database: certificateDatabase.toNativePath(),
                           password: 'dartdart',
                           useBuiltinRoots: false);
   test(false, false);
   test(true, false);
   test(false, true);
   test(true, true);
   test(false, true, true);
   test(true, true, true);
 }