Add chain support to barback.

pkg/barback/lib/src/pool.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.pool;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:stack_trace/stack_trace.dart';
 
+import 'utils.dart';
+
 // TODO(nweiz): put this somewhere that it can be shared between packages.
 /// Manages an abstract pool of resources with a limit on how many may be in use
 /// at once.
 ///
 /// When a resource is needed, the user should call [request]. When the returned
 /// future completes with a [PoolResource], the resource may be allocated. Once
 /// the resource has been released, the user should call [PoolResource.release].
 /// The pool will ensure that only a certain number of [PoolResource]s may be
 /// allocated at once.
 class Pool {
@@ skipping 45 matching lines @@
       return completer.future;
     }
   }
 
   /// Requests a resource for the duration of [callback], which may return a
   /// Future.
   ///
   /// The return value of [callback] is piped to the returned Future.
   Future withResource(callback()) {
     return request().then((resource) =>
-        new Future.sync(callback).whenComplete(resource.release));
+        syncFuture(callback).whenComplete(resource.release));
   }
 
   /// If there are any pending requests, this will fire the oldest one.
   void _onResourceReleased() {
     if (_requestedResources.isEmpty) {
       _allocatedResources--;
       if (_timer != null) {
         _timer.cancel();
         _timer = null;
       }
@@ skipping 13 matching lines @@
     } else {
       _timer = new Timer(_timeout, _onTimeout);
     }
   }
 
   /// Handles [_timer] timing out by causing all pending resource completers to
   /// emit exceptions.
   void _onTimeout() {
     for (var completer in _requestedResources) {
       completer.completeError("Pool deadlock: all resources have been "
-          "allocated for too long.", new Trace.current().vmTrace);
+          "allocated for too long.", new Chain.current());
     }
     _requestedResources.clear();
     _timer = null;
   }
 }
 
 /// A member of a [Pool].
 ///
 /// A [PoolResource] is a token that indicates that a resource is allocated.
 /// When the associated resource is released, the user should call [release].
 class PoolResource {
   final Pool _pool;
 
   /// Whether [this] has been released yet.
   bool _released = false;
 
   PoolResource._(this._pool);
 
   /// Tells the parent [Pool] that the resource associated with this resource is
   /// no longer allocated, and that a new [PoolResource] may be allocated.
   void release() {
     if (_released) {
       throw new StateError("A PoolResource may only be released once.");
     }
     _released = true;
     _pool._onResourceReleased();
   }
 }