Bring in the latest version of the SDK's WebSocket impl.

lib/src/copy/io_sink.dart

 // Copyright (c) 2015, 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.
 
 // The following code is copied from sdk/lib/io/io_sink.dart. The "dart:io"
 // implementation isn't used directly to support non-"dart:io" applications.
 //
 // Because it's copied directly, only modifications necessary to support the
 // desired public API and to remove "dart:io" dependencies have been made.
 //
 // This is up-to-date as of sdk revision
-// 86227840d75d974feb238f8b3c59c038b99c05cf.
+// e41fb4cafd6052157dbc1490d437045240f4773f.
+
 import 'dart:async';
 
 class StreamSinkImpl<T> implements StreamSink<T> {
   final StreamConsumer<T> _target;
-  Completer _doneCompleter = new Completer();
-  Future _doneFuture;
+  final Completer _doneCompleter = new Completer();
   StreamController<T> _controllerInstance;
   Completer _controllerCompleter;
   bool _isClosed = false;
   bool _isBound = false;
   bool _hasError = false;
 
-  StreamSinkImpl(this._target) {
-    _doneFuture = _doneCompleter.future;
-  }
+  StreamSinkImpl(this._target);
 
   void add(T data) {
     if (_isClosed) return;
     _controller.add(data);
   }
 
   void addError(error, [StackTrace stackTrace]) {
     _controller.addError(error, stackTrace);
   }
 
@@ skipping 20 matching lines @@
     if (_isBound) {
       throw new StateError("StreamSink is bound to a stream");
     }
     if (_controllerInstance == null) return new Future.value(this);
     // Adding an empty stream-controller will return a future that will complete
     // when all data is done.
     _isBound = true;
     var future = _controllerCompleter.future;
     _controllerInstance.close();
     return future.whenComplete(() {
-          _isBound = false;
-        });
+      _isBound = false;
+    });
   }
 
   Future close() {
     if (_isBound) {
       throw new StateError("StreamSink is bound to a stream");
     }
     if (!_isClosed) {
       _isClosed = true;
       if (_controllerInstance != null) {
         _controllerInstance.close();
       } else {
         _closeTarget();
       }
     }
     return done;
   }
 
   void _closeTarget() {
     _target.close().then(_completeDoneValue, onError: _completeDoneError);
   }
 
-  Future get done => _doneFuture;
+  Future get done => _doneCompleter.future;
 
   void _completeDoneValue(value) {
-    if (_doneCompleter == null) return;
-    _doneCompleter.complete(value);
-    _doneCompleter = null;
+    if (!_doneCompleter.isCompleted) {
+      _doneCompleter.complete(value);
+    }
   }
 
   void _completeDoneError(error, StackTrace stackTrace) {
-    if (_doneCompleter == null) return;
-    _hasError = true;
-    _doneCompleter.completeError(error, stackTrace);
-    _doneCompleter = null;
+    if (!_doneCompleter.isCompleted) {
+      _hasError = true;
+      _doneCompleter.completeError(error, stackTrace);
+    }
   }
 
   StreamController<T> get _controller {
     if (_isBound) {
       throw new StateError("StreamSink is bound to a stream");
     }
     if (_isClosed) {
       throw new StateError("StreamSink is closed");
     }
     if (_controllerInstance == null) {
       _controllerInstance = new StreamController<T>(sync: true);
       _controllerCompleter = new Completer();
-      _target.addStream(_controller.stream)
-          .then(
-              (_) {
-                if (_isBound) {
-                  // A new stream takes over - forward values to that stream.
-                  _controllerCompleter.complete(this);
-                  _controllerCompleter = null;
-                  _controllerInstance = null;
-                } else {
-                  // No new stream, .close was called. Close _target.
-                  _closeTarget();
-                }
-              },
-              onError: (error, stackTrace) {
-                if (_isBound) {
-                  // A new stream takes over - forward errors to that stream.
-                  _controllerCompleter.completeError(error, stackTrace);
-                  _controllerCompleter = null;
-                  _controllerInstance = null;
-                } else {
-                  // No new stream. No need to close target, as it have already
-                  // failed.
-                  _completeDoneError(error, stackTrace);
-                }
-              });
-    }
+      _target.addStream(_controller.stream).then((_) {
+        if (_isBound) {
+          // A new stream takes over - forward values to that stream.
+          _controllerCompleter.complete(this);
+          _controllerCompleter = null;
+          _controllerInstance = null;
+        } else {
+          // No new stream, .close was called. Close _target.
+          _closeTarget();
+        }
+      }, onError: (error, stackTrace) {
+        if (_isBound) {
+          // A new stream takes over - forward errors to that stream.
+          _controllerCompleter.completeError(error, stackTrace);
+          _controllerCompleter = null;
+          _controllerInstance = null;
+        } else {
+          // No new stream. No need to close target, as it has already
+          // failed.
+          _completeDoneError(error, stackTrace);
+        }
+      });
+   }
     return _controllerInstance;
   }
 }
-