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

sdk/lib/io/io_sink.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.
 
 part of dart.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by all [StringSink] methods and will delay
  * a [addStream] until the buffer is flushed.
  *
  * When the [IOSink] is bound to a stream (through [addStream]) any call
- * to the [IOSink] will throw a [StateError]. When the [addStream] compeltes,
+ * to the [IOSink] will throw a [StateError]. When the [addStream] completes,
  * the [IOSink] will again be open for all calls.
+ *
+ * If data is added to the [IOSink] after the sink is closed, the data will be
+ * ignored. Use the [done] future to be notified when the [IOSink] is closed.
  */
 abstract class IOSink implements StreamSink<List<int>>, StringSink {
   factory IOSink(StreamConsumer<List<int>> target,
                  {Encoding encoding: Encoding.UTF_8})
       => new _IOSinkImpl(target, encoding);
 
   /**
    * The [Encoding] used when writing strings. Depending on the
    * underlying consumer this property might be mutable.
    */
@@ skipping 36 matching lines @@
   Completer _controllerCompleter;
   bool _isClosed = false;
   bool _isBound = false;
   bool _hasError = false;
 
   _StreamSinkImpl(StreamConsumer<T> this._target) {
     _doneFuture = _doneCompleter.future;
   }
 
   void add(T data) {
+    if (_isClosed) return;
     _controller.add(data);
   }
 
   void addError(error) {
     _controller.addError(error);
   }
 
   Future addStream(Stream<T> stream) {
     if (_isBound) {
       throw new StateError("StreamSink is already bound to a stream");
@@ skipping 139 matching lines @@
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   void writeCharCode(int charCode) {
     write(new String.fromCharCode(charCode));
   }
 }