Make pkg/stack_trace use stack chains.

pkg/scheduled_test/lib/src/descriptor/file_descriptor.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 descriptor.file;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:path/path.dart' as path;
+import 'package:stack_trace/stack_trace.dart';
 
 import '../../descriptor.dart';
 import '../../scheduled_test.dart';
 import '../utils.dart';
 
 /// A descriptor describing a single file.
 abstract class FileDescriptor extends Descriptor implements ReadableDescriptor {
   /// The contents of the file, in bytes.
   final List<int> contents;
 
@@ skipping 19 matching lines @@
 
   /// Creates a new text [FileDescriptor] with [name] and [contents].
   factory FileDescriptor(String name, String contents) =>
     new _StringFileDescriptor(name, contents);
 
   FileDescriptor._(String name, this.contents)
       : super(name);
 
   Future create([String parent]) => schedule(() {
     if (parent == null) parent = defaultRoot;
-    return new File(path.join(parent, name)).writeAsBytes(contents);
+    return Chain.track(new File(path.join(parent, name))
+        .writeAsBytes(contents));
   }, "creating file '$name'");
 
   Future validate([String parent]) =>
     schedule(() => validateNow(parent), "validating file '$name'");
 
   Future validateNow([String parent]) {
     if (parent == null) parent = defaultRoot;
     var fullPath = path.join(parent, name);
     if (!new File(fullPath).existsSync()) {
       fail("File not found: '$fullPath'.");
     }
 
-    return new File(fullPath).readAsBytes().then(_validateNow);
+    return Chain.track(new File(fullPath).readAsBytes()).then(_validateNow);
   }
 
   // TODO(nweiz): rather than setting up an inheritance chain, just store a
   // Matcher for validation. This would require better error messages from the
   // matcher library, though.
   /// A function that throws an error if [binaryContents] doesn't match the
   /// expected contents of the descriptor.
   void _validateNow(List<int> binaryContents);
 
   Stream<List<int>> read() => new Future.value(contents).asStream();
@@ skipping 64 matching lines @@
 
   _MatcherFileDescriptor(String name, this._matcher, {bool isBinary})
       : _isBinary = isBinary == true ? true : false,
         super._(name, <int>[]);
 
   void _validateNow(List<int> actualContents) =>
       expect(
           _isBinary ? actualContents : new String.fromCharCodes(actualContents),
           _matcher);
 }