Make new StreamController be async by default.

sdk/lib/_internal/pub/lib/src/io.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.
 
 /// Helper functionality to make working with IO easier.
 library pub.io;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
@@ skipping 404 matching lines @@
 /// Reads and discards all output from [stream]. Returns a [Future] that
 /// completes when the stream is closed.
 Future drainStream(Stream stream) {
   return stream.fold(null, (x, y) {});
 }
 
 /// Returns a [EventSink] that pipes all data to [consumer] and a [Future] that
 /// will succeed when [EventSink] is closed or fail with any errors that occur
 /// while writing.
 Pair<EventSink, Future> consumerToSink(StreamConsumer consumer) {
-  var controller = new StreamController();
+  var controller = new StreamController(sync: true);
   var done = controller.stream.pipe(consumer);
   return new Pair<EventSink, Future>(controller.sink, done);
 }
 
 // TODO(nweiz): remove this when issue 7786 is fixed.
 /// Pipes all data and errors from [stream] into [sink]. When [stream] is done,
 /// the returned [Future] is completed and [sink] is closed if [closeSink] is
 /// true.
 ///
 /// When an error occurs on [stream], that error is passed to [sink]. If
@@ skipping 296 matching lines @@
 /// Create a .tar.gz archive from a list of entries. Each entry can be a
 /// [String], [Directory], or [File] object. The root of the archive is
 /// considered to be [baseDir], which defaults to the current working directory.
 /// Returns a [ByteStream] that will emit the contents of the archive.
 ByteStream createTarGz(List contents, {baseDir}) {
   var buffer = new StringBuffer();
   buffer.write('Creating .tag.gz stream containing:\n');
   contents.forEach((file) => buffer.write('$file\n'));
   log.fine(buffer.toString());
 
-  var controller = new StreamController<List<int>>();
+  var controller = new StreamController<List<int>>(sync: true);
 
   if (baseDir == null) baseDir = path.current;
   baseDir = path.absolute(baseDir);
   contents = contents.map((entry) {
     entry = path.absolute(entry);
     if (!isBeneath(entry, baseDir)) {
       throw new ArgumentError('Entry $entry is not inside $baseDir.');
     }
     return path.relative(entry, from: baseDir);
   }).toList();
@@ skipping 65 matching lines @@
   const PubProcessResult(this.stdout, this.stderr, this.exitCode);
 
   bool get success => exitCode == 0;
 }
 
 /// Gets a [Uri] for [uri], which can either already be one, or be a [String].
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return Uri.parse(uri);
 }