Provide more error-handling customization.

lib/src/stream_channel_controller.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 
 import '../stream_channel.dart';
 
 /// A controller for exposing a new [StreamChannel].
 ///
@@ skipping 29 matching lines @@
   /// This channel should be returned to external users so they can communicate
   /// with [local].
   StreamChannel<T> get foreign => _foreign;
   StreamChannel<T> _foreign;
 
   /// Creates a [StreamChannelController].
   ///
   /// If [sync] is true, events added to either channel's sink are synchronously
   /// dispatched to the other channel's stream. This should only be done if the
   /// source of those events is already asynchronous.
-  StreamChannelController({bool sync: false}) {
+  ///
+  /// If [allowForeignErrors] is `false`, errors are not allowed to be passed to
+  /// the foreign channel's sink. If any are, the connection will close and the
+  /// error will be forwarded to the foreign channel's [Sink.done] future. This
+  /// guarantees that the local stream will never emit errors.
+  StreamChannelController({bool allowForeignErrors: true, bool sync: false}) {
     var localToForeignController = new StreamController<T>(sync: sync);
     var foreignToLocalController = new StreamController<T>(sync: sync);
     _local = new StreamChannel<T>.withGuarantees(
         foreignToLocalController.stream, localToForeignController.sink);
     _foreign = new StreamChannel<T>.withGuarantees(
-        localToForeignController.stream, foreignToLocalController.sink);
+        localToForeignController.stream, foreignToLocalController.sink,
+        allowSinkErrors: allowForeignErrors);
   }
 }