Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

pkg/scheduled_test/lib/src/schedule.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 schedule;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 330 matching lines @@
 
   const ScheduleState._(this.name);
 
   String toString() => name;
 }
 
 /// A queue of asynchronous tasks to execute in order.
 class TaskQueue {
   // TODO(nweiz): make this a read-only view when issue 8321 is fixed.
   /// The tasks in the queue.
-  Collection<Task> get contents => _contents;
+  Iterable<Task> get contents => _contents;
   final _contents = new Queue<Task>();
 
   /// The name of the queue, for debugging purposes.
   final String name;
 
   /// If `true`, then new [Task]s in this queue will capture the current stack
   /// trace before running.
   bool get captureStackTraces => _schedule.captureStackTraces;
 
   /// The [Schedule] that created this queue.
@@ skipping 11 matching lines @@
   /// The toal number of out-of-band callbacks that have been registered on
   /// [this].
   int _totalCallbacks = 0;
 
   /// Whether to stop running after the current task.
   bool _aborted = false;
 
   // TODO(nweiz): make this a read-only view when issue 8321 is fixed.
   /// The descriptions of all callbacks that are blocking the completion of
   /// [this].
-  Collection<String> get pendingCallbacks => _pendingCallbacks;
+  Iterable<String> get pendingCallbacks => _pendingCallbacks;
   final _pendingCallbacks = new Queue<String>();
 
   /// A completer that will be completed once [_pendingCallbacks] becomes empty
   /// after the queue finishes running its tasks.
   Future get _noPendingCallbacks => _noPendingCallbacksCompleter.future;
   final Completer _noPendingCallbacksCompleter = new Completer();
 
   /// A [Future] that completes when the tasks in [this] are all complete. If an
   /// error occurs while running this queue, the returned [Future] will complete
   /// with that error.
@@ skipping 204 matching lines @@
           return prefixLines(childString,
               firstPrefix: "  $prefix ", prefix: "  | ");
         }).join('\n');
         taskString = '$taskString\n$childrenString';
       }
 
       return taskString;
     }).join("\n");
   }
 }