Ensure that errors have stack traces attached.

pkg/scheduled_test/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 utils;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 10 matching lines @@
     if (other is! Pair) return false;
     return other.first == first && other.last == last;
   }
 
   int get hashCode => first.hashCode ^ last.hashCode;
 }
 
 /// Configures [future] so that its result (success or exception) is passed on
 /// to [completer].
 void chainToCompleter(Future future, Completer completer) {
-  future.then((value) => completer.complete(value),
-      onError: completer.completeError);
+  future.then(completer.complete, onError: completer.completeError);
 }
 
 /// 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) {
     return lines.map((line) => '$prefix$line').join('\n');
   }
 
@@ skipping 189 matching lines @@
 }
 
 /// Returns a string representation of [trace] that has the core and test frames
 /// folded together.
 String terseTraceString(StackTrace trace) {
   return new Trace.from(trace).terse.foldFrames((frame) {
     return frame.package == 'scheduled_test' || frame.package == 'unittest' ||
         frame.isCore;
   }).toString().trim();
 }