Revert "Add built-in timeouts to scheduled_test."

pkg/scheduled_test/lib/src/substitute_future.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 substitute_future;
-
-import 'dart:async';
-
-/// A wrapper for [Future] that allows other [Future]s to be substituted in as
-/// the wrapped [Future]. This is used for injecting timeout errors into
-/// long-running [Future]s.
-class SubstituteFuture<T> implements Future<T> {
-  /// The wrapped [Future].
-  Future<T> _inner;
-
-  /// The completer that corresponds to [this]'s result.
-  final Completer<T> _completer = new Completer<T>();
-
-  /// Whether or not [this] has been completed yet.
-  bool _complete = false;
-
-  SubstituteFuture(Future wrapped) {
-    substitute(wrapped);
-  }
-
-  Stream<T> asStream() => _completer.future.asStream();
-  Future catchError(onError(AsyncError asyncError), {bool test(error)}) =>
-    _completer.future.catchError(onError, test: test);
-  Future then(onValue(T value), {onError(AsyncError asyncError)}) =>
-    _completer.future.then(onValue, onError: onError);
-  Future<T> whenComplete(action()) => _completer.future.whenComplete(action);
-
-  /// Substitutes [newFuture] for the currently wrapped [Future], which is
-  /// returned.
-  Future<T> substitute(Future<T> newFuture) {
-    if (_complete) {
-      throw new StateError("You may not call substitute on a SubstituteFuture "
-          "that's already complete.");
-    }
-
-    var oldFuture = _inner;
-    _inner = newFuture;
-    _inner.then((value) {
-      if (_inner != newFuture) return;
-      _completer.complete(value);
-      _complete = true;
-    }).catchError((error) {
-      if (_inner != newFuture) return;
-      _completer.completeError(error);
-      _complete = true;
-    });
-    return oldFuture;
-  }
-}