Use UnmodifiableListView to expose read-only lists.

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';
 
 import '../scheduled_test.dart' show currentSchedule;
 import 'future_group.dart';
 import 'schedule.dart';
 import 'utils.dart';
 
 typedef Future TaskBody();
 
 /// A single task to be run as part of a [TaskQueue].
 ///
 /// There are two levels of tasks. **Top-level tasks** are created by calling
 /// [TaskQueue.schedule] before the queue in question is running. They're run in
 /// sequence as part of that [TaskQueue]. **Nested tasks** are created by
 /// calling [TaskQueue.schedule] once the queue is already running, and are run
 /// in parallel as part of a top-level task.
 class Task {
   /// The queue to which this [Task] belongs.
   final TaskQueue queue;
 
-  // TODO(nweiz): make this a read-only view when issue 8321 is fixed.
   /// Child tasks that have been spawned while running this task. This will be
   /// empty if this task is a nested task.
-  final children = new Queue<Task>();
+  List<Task> get children => new UnmodifiableListView(_children);
+  final _children = new Queue<Task>();
 
   /// A [FutureGroup] that will complete once all current child tasks are
   /// finished running. This will be null if no child tasks are currently
   /// running.
   FutureGroup _childGroup;
 
   /// A description of this task. Used for debugging. May be `null`.
   final String description;
 
   /// The parent task, if this is a nested task that was started while another
@@ skipping 59 matching lines @@
       _state = TaskState.ERROR;
       throw e;
     }).catchError((_) {});
   }
 
   /// Run [fn] as a child of this task. Returns a Future that will complete with
   /// the result of the child task. This task will not complete until [fn] has
   /// finished.
   Future runChild(fn(), String description) {
     var task = new Task._child(fn, description, this);
-    children.add(task);
+    _children.add(task);
     if (_childGroup == null || _childGroup.completed) {
       _childGroup = new FutureGroup();
     }
     // 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;
   }
 
@@ skipping 30 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;
 }