Add chain support to barback.

pkg/barback/lib/src/utils.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.
 
 library barback.utils;
 
 import 'dart:async';
 import 'dart:typed_data';
 
+import 'package:stack_trace/stack_trace.dart';
+
 /// A pair of values.
 class Pair<E, F> {
   E first;
   F last;
 
   Pair(this.first, this.last);
 
   String toString() => '($first, $last)';
 
   bool operator==(other) {
@@ skipping 124 matching lines @@
   var doneCount = 0;
   // Use a sync stream to preserve the synchrony behavior of the input streams.
   // If the inputs are sync, then this will be sync as well; if the inputs are
   // async, then the events we receive will also be async, and forwarding them
   // sync won't change that.
   var controller = broadcast ? new StreamController.broadcast(sync: true)
       : new StreamController(sync: true);
 
   for (var stream in streams) {
     stream.listen(
-      controller.add,
-      onError: controller.addError,
-      onDone: () {
-    doneCount++;
-    if (doneCount == streams.length) controller.close();
-  });
+        controller.add,
+        onError: controller.addError,
+        onDone: () {
+      doneCount++;
+      if (doneCount == streams.length) controller.close();
+    });
   }
 
   return controller.stream;
 }
 
 /// Prepends each line in [text] with [prefix]. If [firstPrefix] is passed, the
 /// first line is prefixed with that instead.
 String prefixLines(String text, {String prefix: '| ', String firstPrefix}) {
   var lines = text.split('\n');
   if (firstPrefix == null) {
@@ skipping 16 matching lines @@
   // would therefore not wait for microtask callbacks that are scheduled after
   // invoking this method.
   return new Future.delayed(Duration.ZERO, () => pumpEventQueue(times - 1));
 }
 
 /// Like `new Future`, but avoids issue 11911 by using `new Future.value` under
 /// the covers.
 // TODO(jmesserly): doc comment changed to due 14601.
 Future newFuture(callback()) => new Future.value().then((_) => callback());
 
+/// Like [Future.sync], but wraps the Future in [Chain.track] as well.
+Future syncFuture(callback()) => Chain.track(new Future.sync(callback));
+
 /// Returns a buffered stream that will emit the same values as the stream
 /// returned by [future] once [future] completes.
 ///
 /// If [future] completes to an error, the return value will emit that error and
 /// then close.
 ///
 /// If [broadcast] is true, a broadcast stream is returned. This assumes that
 /// the stream returned by [future] will be a broadcast stream as well.
 /// [broadcast] defaults to false.
 Stream futureStream(Future<Stream> future, {bool broadcast: false}) {
@@ skipping 45 matching lines @@
     subscription = callback().listen(controller.add,
         onError: controller.addError,
         onDone: controller.close);
   },
       onCancel: () => subscription.cancel(),
       onPause: () => subscription.pause(),
       onResume: () => subscription.resume(),
       sync: true);
   return controller.stream;
 }