Fix warnings in library-tests.

tests/lib/async/stream_transformer_test.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.
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'dart:async';
 import 'event_helper.dart';
 
 _defaultData(x) {}
 _defaultError(e, [st]) {}
 _defaultDone() {}
 
 /// Dummy StreamSubscription.
 class MyStreamSubscription<T> implements StreamSubscription<T> {
   final Stream stream;
   final bool cancelOnError;
   Function handleData = null;
   Function handleError = null;
   Function handleDone = null;
 
   MyStreamSubscription(this.stream, this.cancelOnError);
 
-  void cancel() {}
+  Future cancel() => null;
   void onData(void handleData(T data)) {
     this.handleData = handleData == null ? _defaultData: handleData;
   }
   void onError(Function handleError) {
     this.handleError = handleError == null ? _defaultError: handleError;
   }
   void onDone(void handleDone()) {
     this.handleDone = handleDone == null ? _defaultDone: handleDone;
   }
 
   void pause([Future resumeSignal]) {}
+  void resume() {}
+
   final isPaused = false;
   Future asFuture([var futureValue]) => null;
 }
 
 main() {
   var transformer = new StreamTransformer<int, String> (
     (stream, cancelOnError) => new MyStreamSubscription(stream, cancelOnError));
 
   var controller = new StreamController(sync: true);
   var stream = controller.stream;
@@ skipping 30 matching lines @@
   transformed = stream.transform(transformer);
   subscription =
       transformed.listen(null, onDone: handleDone, cancelOnError: true);
 
   Expect.identical(stream, subscription.stream);
   Expect.equals(true, subscription.cancelOnError);
   Expect.identical(_defaultData, subscription.handleData);
   Expect.identical(_defaultError, subscription.handleError);
   Expect.identical(handleDone, subscription.handleDone);
 }