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

tests/standalone/io/http_10_test.dart

 // (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 11 matching lines @@
       Expect.equals(-1, request.contentLength);
       var response = request.response;
       response.contentLength = 1;
       Expect.equals("1.0", request.protocolVersion);
       response.done
           .then((_) => Expect.fail("Unexpected response completion"))
           .catchError((error) => Expect.isTrue(error is HttpException));
       response.write("Z");
       response.write("Z");
       response.close();
-      Expect.throws(() {
-        response.write("x");
-      }, (e) => e is StateError);
+      response.write("x");
     }, onError: (e, trace) {
       String msg = "Unexpected error $e";
       if (trace != null) msg += "\nStackTrace: $trace";
       Expect.fail(msg);
     });
 
     int count = 0;
     makeRequest() {
       Socket.connect("127.0.0.1", server.port).then((socket) {
         socket.write("GET / HTTP/1.0\r\n\r\n");
@@ skipping 161 matching lines @@
     makeRequest();
   });
 }
 
 void main() {
   testHttp10NoKeepAlive();
   testHttp10ServerClose();
   testHttp10KeepAlive();
   testHttp10KeepAliveServerCloses();
 }