Fix warnings in library-tests.

tests/lib/convert/chunked_conversion1_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 'dart:convert';
 
 import 'package:expect/expect.dart';
 
 // This test implements a new special interface that can be used to
 // send data more efficiently between two converters.
@@ skipping 14 matching lines @@
 }
 
 class IntAdapterSink extends MyChunkedIntSink {
   final _sink;
   IntAdapterSink(this._sink);
   add(o) => _sink.add(o);
   close() => _sink.close();
   specialI(o) => add(o);
 }
 
-class MyChunkedBoolSink extends ChunkedConversionSink<bool> {
+abstract class MyChunkedBoolSink extends ChunkedConversionSink<bool> {
   MyChunkedBoolSink();
   factory MyChunkedBoolSink.from(sink) = BoolAdapterSink;
   factory MyChunkedBoolSink.withCallback(callback) {
     var sink = new ChunkedConversionSink.withCallback(callback);
     return new MyChunkedBoolSink.from(sink);
   }
 
   add(bool b);
   close();
 
@@ skipping 199 matching lines @@
   intSink.add(-3);
   intSink.add(3);
   intSink.close();
   Expect.isTrue(hasExecuted);
   Expect.equals(0, specialBCounter);
   specialBCounter = 0;
   Expect.equals(1, specialICounter);
   specialICounter = 0;
   hasExecuted = false;
 }