Make IsolateChannel's controllers synchronous.

This is slightly more efficient, and also make it easier for other
packages to work around dart-lang/sdkdart-lang/stream_channel#25745.

R=tjblasi@google.com

Review URL: https://codereview.chromium.org//1690473002 .

pkgs/stream_channel/CHANGELOG.md

diff --git a/pkgs/stream_channel/CHANGELOG.md b/pkgs/stream_channel/CHANGELOG.md
index dd74936..05a83e0 100644
--- a/pkgs/stream_channel/CHANGELOG.md
+++ b/pkgs/stream_channel/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.3.1
+
+* Make `IsolateChannel` slightly more efficient.
+
 ## 1.3.0
 
 * Add `Disconnector`, a transformer that allows the caller to disconnect the

pkgs/stream_channel/lib/src/isolate_channel.dart

diff --git a/pkgs/stream_channel/lib/src/isolate_channel.dart b/pkgs/stream_channel/lib/src/isolate_channel.dart
index 3466d19..dcb52cb 100644
--- a/pkgs/stream_channel/lib/src/isolate_channel.dart
+++ b/pkgs/stream_channel/lib/src/isolate_channel.dart
@@ -53,7 +53,8 @@
     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 +92,8 @@
   /// 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._(

pkgs/stream_channel/pubspec.yaml

diff --git a/pkgs/stream_channel/pubspec.yaml b/pkgs/stream_channel/pubspec.yaml
index c787b95..930f744 100644
--- a/pkgs/stream_channel/pubspec.yaml
+++ b/pkgs/stream_channel/pubspec.yaml
@@ -1,5 +1,5 @@
 name: stream_channel
-version: 1.3.0
+version: 1.3.1-dev
 description: An abstraction for two-way communication channels.
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/stream_channel