Make pkg/stack_trace use stack chains.

pkg/scheduled_test/lib/src/task.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 task;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 43 matching lines @@
   /// task within [queue]; for nested tasks, this is the index within
   /// [parent.children]. It's used for debugging when [description] isn't
   /// provided.
   int _id;
 
   /// A Future that will complete to the return value of [fn] once this task
   /// finishes running.
   Future get result => _resultCompleter.future;
   final _resultCompleter = new Completer();
 
-  final Trace stackTrace;
+  final Chain stackChain;
 
   Task(fn(), String description, TaskQueue queue)
     : this._(fn, description, queue, null, queue.contents.length);
 
   Task._child(fn(), String description, Task parent)
     : this._(fn, description, parent.queue, parent, parent.children.length);
 
   Task._(fn(), this.description, TaskQueue queue, this.parent, this._id)
       : queue = queue,
-        stackTrace = new Trace.current() {
+        stackChain = new Chain.current() {
     this.fn = () {
       if (state != TaskState.WAITING) {
         throw new StateError("Can't run $state task '$this'.");
       }
 
       _state = TaskState.RUNNING;
       var future = new Future.value().then((_) => fn())
           .whenComplete(() {
         if (_childGroup == null || _childGroup.completed) return null;
         return _childGroup.future;
@@ skipping 31 matching lines @@
     // Ignore errors in the FutureGroup; they'll get picked up via wrapFuture,
     // and we don't want them to short-circuit the other Futures.
     _childGroup.add(task.result.catchError((_) {}));
     task.fn();
     return task.result;
   }
 
   String toString() => description == null ? "#$_id" : description;
 
   String toStringWithStackTrace() {
-    var result = toString();
-    if (stackTrace != null) {
-      var stackString = prefixLines(terseTraceString(stackTrace));
-      result += "\n\nStack trace:\n$stackString";
-    }
-    return result;
+    var stackString = prefixLines(terseTraceString(stackChain));
+    return "$this\n\nStack chain:\n$stackString";
   }
 
   /// Returns a detailed representation of [queue] with this task highlighted.
   String generateTree() => queue.generateTree(this);
 }
 
 /// An enum of states for a [Task].
 class TaskState {
   /// The task is waiting to be run.
   static const WAITING = const TaskState._("WAITING");
@@ skipping 11 matching lines @@
   final String name;
 
   /// Whether the state indicates that the task has finished running. This is
   /// true for both the [SUCCESS] and [ERROR] states.
   bool get isDone => this == SUCCESS || this == ERROR;
 
   const TaskState._(this.name);
 
   String toString() => name;
 }