Make new StreamController be async by default.

pkg/http/lib/src/utils.dart

 // Copyright (c) 2012, 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.
 
 library utils;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:typed_data';
 import 'dart:utf';
@@ skipping 155 matching lines @@
 
 /// Returns a [Future] that asynchronously completes to `null`.
 Future get async => new Future.value();
 
 /// Returns a closed [Stream] with no elements.
 Stream get emptyStream => streamFromIterable([]);
 
 /// Creates a single-subscription stream that emits the items in [iter] and then
 /// ends.
 Stream streamFromIterable(Iterable iter) {
-  var controller = new StreamController();
+  var controller = new StreamController(sync: true);
   iter.forEach(controller.add);
   controller.close();
   return controller.stream;
 }
 
 // TODO(nweiz): remove this when issue 7787 is fixed.
 /// Creates two single-subscription [Stream]s that each emit all values and
 /// errors from [stream]. This is useful if [stream] is single-subscription but
 /// multiple subscribers are necessary.
 Pair<Stream, Stream> tee(Stream stream) {
-  var controller1 = new StreamController();
-  var controller2 = new StreamController();
+  var controller1 = new StreamController(sync: true);
+  var controller2 = new StreamController(sync: true);
   stream.listen((value) {
     controller1.add(value);
     controller2.add(value);
   }, onError: (error) {
     controller1.addError(error);
     controller2.addError(error);
   }, onDone: () {
     controller1.close();
     controller2.close();
   });
@@ skipping 34 matching lines @@
 /// The return values of all [Future]s are discarded. Any errors will cause the
 /// iteration to stop and will be piped through the return value.
 Future forEachFuture(Iterable input, Future fn(element)) {
   var iterator = input.iterator;
   Future nextElement(_) {
     if (!iterator.moveNext()) return new Future.value();
     return fn(iterator.current).then(nextElement);
   }
   return nextElement(null);
 }