Remove deprecated parts of dart:async.

pkg/barback/lib/src/build_result.dart

Index: pkg/barback/lib/src/build_result.dart
diff --git a/pkg/barback/lib/src/build_result.dart b/pkg/barback/lib/src/build_result.dart
index 65e82690ccc9f9ea23015fc44b745b61b650db47..763ac2b9044f7ad4ec1bc5d790b26554ae33c2db 100644
--- a/pkg/barback/lib/src/build_result.dart
+++ b/pkg/barback/lib/src/build_result.dart
@@ -47,7 +47,7 @@ class BuildResult {
     if (succeeded) return "success";
 
     return "errors:\n" + errors.map((error) {
-      var stackTrace = getAttachedStackTrace(error);
+      var stackTrace = error.stackTrace;

[nweiz, 2013/10/30 22:48:18]

Most BarbackErrors don't have a [stackTrace] property. We should check if this
is a [TransformerException] or an [AssetLoadException].

[floitsch, 2013/10/31 00:38:14]

Done.

       if (stackTrace != null) stackTrace = new Trace.from(stackTrace);
 
       var msg = new StringBuffer();