Revert "Throw when adding something to a closed sink and improve documentation."

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
 // OtherResources=certificates/server_chain.pem
 // OtherResources=certificates/server_key.pem
@@ skipping 146 matching lines @@
     if (!handshakeBeforeSecure) {
       return Socket.connect(HOST, port).then((socket) {
         var future;
         if (hostnameInConnect) {
           future = SecureSocket.secure(socket, context: clientContext);
         } else {
           future =
               SecureSocket.secure(socket, host: HOST, context: clientContext);
         }
         return future.then((secureSocket) {
-          Expect.throws(() {
-            socket.add([0]);
-          });
+          socket.add([0]);
           return secureSocket;
         });
       });
     } else {
       return Socket.connect(HOST, port).then((socket) {
         return runClientHandshake(socket).then((_) {
           var future;
           if (hostnameInConnect) {
             future = SecureSocket.secure(socket, context: clientContext);
           } else {
             future =
                 SecureSocket.secure(socket, host: HOST, context: clientContext);
           }
           return future.then((secureSocket) {
-            Expect.throws(() {
-              socket.add([0]);
-            });
+            socket.add([0]);
             return secureSocket;
           });
         });
       });
     }
   }
 
   serverReady(server) {
     server.listen((client) {
       if (!handshakeBeforeSecure) {
         SecureSocket.secureServer(client, serverContext).then((secureClient) {
-          Expect.throws(() {
-            client.add([0]);
-          });
+          client.add([0]);
           runServer(secureClient).then((_) => server.close());
         });
       } else {
         runServerHandshake(client).then((carryOverData) {
           SecureSocket
               .secureServer(client, serverContext, bufferedData: carryOverData)
               .then((secureClient) {
-            Expect.throws(() {
-              client.add([0]);
-            });
+            client.add([0]);
             runServer(secureClient).then((_) => server.close());
           });
         });
       }
     });
 
     connectClient(server.port).then(runClient).then((socket) {
       asyncEnd();
     });
   }
 
   ServerSocket.bind(HOST, 0).then(serverReady);
 }
 
 main() {
   asyncStart();
   InternetAddress.lookup("localhost").then((hosts) {
     HOST = hosts.first;
     test(false, false);
     // TODO(whesse): Enable the test with all argument combinations:
     //  test(true, false);
     //  test(false, true);
     //  test(true, true);
     //  test(false, true, true);
     //  test(true, true, true);
     asyncEnd();
   });
 }