Fix discrepancy between trunk and bleeding edge.

dart/sdk/lib/async/signal.dart

-// Copyright (c) 2012, 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.
-
-// part of dart.async;
-
-/**
- *  A basic asynchronous notification.
- */
-abstract class Signal {
-  factory Signal.delayed(int milliseconds) {
-    var completer = new SignalCompleter();
-    new Timer(milliseconds, (_) => completer.complete());
-    return completer.signal;
-  }
-  /**
-   * The [onComplete] handler is called when the signal completes.
-   *
-   * If the signal is already complete, the [onComplete] handler is called
-   * as soon as possible, but no sooner than the next time an event is fired.
-   */
-  void then(void onComplete());
-}
-
-typedef _SignalCompleteHandler();
-
-/**
- * Simple [Signal] controller that creates a [Signal] and allows completing it.
- */
-class SignalCompleter {
-  final Signal signal;
-  SignalCompleter() : signal = new _SignalImpl();
-  void complete() {
-    _SignalImpl mySignal = signal;
-    mySignal._complete();
-  }
-}
-
-/**
- * Simple Signal implementation receiving its completion from a
- * [SignalCompleter].
- */
-class _SignalImpl implements Signal {
-  /** Single-linked list of "done" event handlers to notify. */
-  _SignalListener _listeners = null;
-
-  /** Whether the signal is already completed. */
-  bool _isComplete = false;
-
-  void then(void onComplete()) {
-    _listeners = new _SignalListener(_listeners, onComplete);
-    if (_isComplete) {
-      // Schedule the done events as soon as the event queue is ready.
-      new Timer(0, (Timer timer) { _sendDone(); });
-    }
-  }
-
-  /**
-   * Complete the signal.
-   *
-   * This immediately notifies all listeners on the signal.
-   */
-  void _complete() {
-    assert(!_isComplete);  // Only complete once.
-    _isComplete = true;
-    _sendDone();
-  }
-
-  /**
-   * Notify all listeners.
-   */
-  void _sendDone() {
-    while (_listeners != null) {
-      _DoneHandler onDone = _listeners.listener;
-      _listeners = _listeners.next;
-      try {
-        onDone();
-      } catch (e, s) {
-        new AsyncError(e, s).throwDelayed();
-      }
-    }
-  }
-}
-
-/** Single-linked list element of the listeners on a [_SignalImpl]. */
-class _SignalListener {
-  _SignalListener next;
-  _SignalCompleteHandler listener;
-  _SignalListener(this.next, this.listener);
-}