Make IsolateChannel's controllers synchronous.

lib/src/isolate_channel.dart

Index: lib/src/isolate_channel.dart
diff --git a/lib/src/isolate_channel.dart b/lib/src/isolate_channel.dart
index 3466d19dd10b98f9b8beea4ec9d9f6280d21a5fa..6f86657359628e1688ee86be93cfa7aca3a93ca9 100644
--- a/lib/src/isolate_channel.dart
+++ b/lib/src/isolate_channel.dart
@@ -10,6 +10,8 @@ import 'package:stack_trace/stack_trace.dart';
 
 import '../stream_channel.dart';
 
+import 'dart:io';
+
 /// A [StreamChannel] that communicates over a [ReceivePort]/[SendPort] pair,
 /// presumably with another isolate.
 ///
@@ -53,7 +55,8 @@ class IsolateChannel<T> extends StreamChannelMixin<T> {
     var subscription;
     subscription = receivePort.listen((message) {
       if (message is SendPort) {
-        var controller = new StreamChannelController(allowForeignErrors: false);
+        var controller = new StreamChannelController(
+            allowForeignErrors: false, sync: true);
         new SubscriptionStream<T>(subscription).pipe(controller.local.sink);
         controller.local.stream.listen(message.send,
             onDone: receivePort.close);
@@ -91,7 +94,8 @@ class IsolateChannel<T> extends StreamChannelMixin<T> {
   /// Creates a stream channel that receives messages from [receivePort] and
   /// sends them over [sendPort].
   factory IsolateChannel(ReceivePort receivePort, SendPort sendPort) {
-    var controller = new StreamChannelController(allowForeignErrors: false);
+    var controller = new StreamChannelController(
+        allowForeignErrors: false, sync: true);
     receivePort.pipe(controller.local.sink);
     controller.local.stream.listen(sendPort.send, onDone: receivePort.close);
     return new IsolateChannel._(