Use the async package's CancelableOperation.

lib/src/runner/browser/dartium.dart

 // Copyright (c) 2015, 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 test.runner.browser.dartium;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:async/async.dart';
 import 'package:path/path.dart' as p;
 
-import '../../util/cancelable_future.dart';
 import '../../util/io.dart';
 import '../../utils.dart';
 import 'browser.dart';
 
 final _observatoryRegExp = new RegExp(r"^Observatory listening on ([^ ]+)");
 
 /// A class for running an instance of Dartium.
 ///
 /// Most of the communication with the browser is expected to happen via HTTP,
 /// so this exposes a bare-bones API. The browser starts as soon as the class is
@@ skipping 89 matching lines @@
   /// ordering isn't guaranteed, so we need to figure out which one is correct.
   /// We do so by connecting to the VM service via WebSockets and looking for
   /// the Observatory instance that actually contains an isolate, and returning
   /// the corresponding URI.
   static Future<Uri> _getObservatoryUrl(Stream<List<int>> stdout) async {
     var urlQueue = new StreamQueue(lineSplitter.bind(stdout).map((line) {
       var match = _observatoryRegExp.firstMatch(line);
       return match == null ? null : Uri.parse(match[1]);
     }).where((line) => line != null));
 
-    var futures = [
+    var operations = [
       urlQueue.next,
       urlQueue.next,
       urlQueue.next
     ].map(_checkObservatoryUrl);
 
     urlQueue.cancel();
 
     /// Dartium will print three possible observatory URLs. For each one, we
     /// check whether it's actually connected to an isolate, indicating that
     /// it's the observatory for the main page. Once we find the one that is, we
     /// cancel the other requests and return it.
-    return inCompletionOrder(futures)
+    return inCompletionOrder(operations)
         .firstWhere((url) => url != null, defaultValue: () => null);
   }
 
   /// If the URL returned by [future] corresponds to the correct Observatory
   /// instance, returns it. Otherwise, returns `null`.
   ///
-  /// If the returned future is canceled before it fires, the WebSocket
+  /// If the returned operation is canceled before it fires, the WebSocket
   /// connection with the given Observatory will be closed immediately.
-  static CancelableFuture<Uri> _checkObservatoryUrl(Future<Uri> future) {
+  static CancelableOperation<Uri> _checkObservatoryUrl(Future<Uri> future) {
     var webSocket;
     var canceled = false;
-    var completer = new CancelableCompleter(() {
+    var completer = new CancelableCompleter(onCancel: () {
       canceled = true;
       if (webSocket != null) webSocket.close();
     });
 
     // We've encountered a format we don't understand. Close the web socket and
     // complete to null.
     giveUp() {
       webSocket.close();
       if (!completer.isCompleted) completer.complete();
     }
@@ skipping 82 matching lines @@
         });
       } on IOException catch (_) {
         // IO exceptions are probably caused by connecting to an
         // incorrect WebSocket that already closed.
         return null;
       }
     }).catchError((error, stackTrace) {
       if (!completer.isCompleted) completer.completeError(error, stackTrace);
     });
 
-    return completer.future;
+    return completer.operation;
   }
 }