Adding to a closed sink throws.

tests/standalone/io/http_content_length_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 19 matching lines @@
       });
       // write with content length 0 closes the connection and
       // reports an error.
       response.write("x");
       // Subsequent write are ignored as there is already an
       // error.
       response.write("x");
       // After an explicit close, write becomes a state error
       // because we have said we will not add more.
       response.close();
-      response.write("x");
+      Expect.throws(() {
+        response.write("x");
+      }, (e) => e is StateError);
     }, onError: (e, trace) {
       String msg = "Unexpected server error $e";
       if (trace != null) msg += "\nStackTrace: $trace";
       Expect.fail(msg);
     });
 
     HttpClient client = new HttpClient();
     for (int i = 0; i < totalConnections; i++) {
       client.get("127.0.0.1", server.port, "/").then((request) {
         if (explicitContentLength) {
@@ skipping 31 matching lines @@
         response.write("x");
         response.done.then((_) {
           Expect.fail("Unexpected successful response completion");
         }).catchError((error) {
           Expect.isTrue(error is HttpException, "[$error]");
           if (++serverCount == totalConnections) {
             server.close();
           }
         });
         response.close();
-        response.write("x");
+        Expect.throws(() {
+          response.write("x");
+        }, (e) => e is StateError);
       });
     }, onError: (e, trace) {
       String msg = "Unexpected error $e";
       if (trace != null) msg += "\nStackTrace: $trace";
       Expect.fail(msg);
     });
 
     int clientCount = 0;
     HttpClient client = new HttpClient();
     for (int i = 0; i < totalConnections; i++) {
@@ skipping 39 matching lines @@
         response.headers.set("content-length", 2);
         response.headers.set("transfer-encoding", "chunked");
       }
       request.listen((d) {}, onDone: () {
         response.write("x");
         Expect.throws(() => response.headers.chunkedTransferEncoding = false,
             (e) => e is HttpException);
         response.write("x");
         response.write("x");
         response.close();
-        response.write("x");
+        Expect.throws(() {
+          response.write("x");
+        }, (e) => e is StateError);
       });
     }, onError: (e, trace) {
       String msg = "Unexpected error $e";
       if (trace != null) msg += "\nStackTrace: $trace";
       Expect.fail(msg);
     });
 
     int count = 0;
     HttpClient client = new HttpClient();
     for (int i = 0; i < totalConnections; i++) {
@@ skipping 59 matching lines @@
   testNoBody(5, false);
   testNoBody(25, false);
   testNoBody(5, true);
   testNoBody(25, true);
   testBody(5, false);
   testBody(5, true);
   testBodyChunked(5, false);
   testBodyChunked(5, true);
   testSetContentLength();
 }