Make pkg/stack_trace use stack chains.

pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart

Index: pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart
diff --git a/pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart b/pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart
index 590a1ce140afe3c32c750ded8664fbbdae2c5fe3..8303117a1d948aec7108be0780dddf9465e84fa5 100644
--- a/pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart
+++ b/pkg/scheduled_test/lib/src/descriptor/nothing_descriptor.dart
@@ -11,6 +11,7 @@ import 'package:path/path.dart' as path;
 
 import '../../descriptor.dart';
 import '../../scheduled_test.dart';
+import '../utils.dart';
 
 /// A descriptor that validates that no file exists with the given name.
 /// Creating this descriptor is a no-op and loading from it is invalid.
@@ -23,7 +24,7 @@ class NothingDescriptor extends Descriptor {
   Future validate([String parent]) => schedule(() => validateNow(parent),
       "validating '$name' doesn't exist");
 
-  Future validateNow([String parent]) => new Future.sync(() {
+  Future validateNow([String parent]) => syncFuture(() {
     if (parent == null) parent = defaultRoot;
     var fullPath = path.join(parent, name);
     if (new File(fullPath).existsSync()) {