Make pub strong-mode clean.

lib/src/barback/barback_server.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:async';
 import 'dart:io';
 
+import 'package:async/async.dart';
 import 'package:barback/barback.dart';
 import 'package:mime/mime.dart';
 import 'package:path/path.dart' as path;
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:stack_trace/stack_trace.dart';
 
 import '../barback.dart';
 import '../io.dart';
 import '../log.dart' as log;
 import '../utils.dart';
@@ skipping 131 matching lines @@
       // "pub serve" is only used as a development server and doesn't require
       // any sort of credentials anyway, this is secure.
       return response.change(
           headers: const {"Access-Control-Allow-Origin": "*"});
     });
   }
 
   /// Returns the body of [asset] as a response to [request].
   Future<shelf.Response> _serveAsset(shelf.Request request, Asset asset) async {
     try {
-      var pair = tee(await validateStream(asset.read()));
-      var responseStream = pair.first;
-      var hashStream = pair.last;
+      var streams = StreamSplitter.splitFrom(
+          await validateStream(asset.read()));
+      var responseStream = streams.first;
+      var hashStream = streams.last;
 
       // Allow the asset to be cached based on its content hash.
       var assetSha = await sha1Stream(hashStream);
       var previousSha = request.headers["if-none-match"];
 
       var headers = {
         // Enable browser caching of the asset.
         "ETag": assetSha
       };
 
@@ skipping 56 matching lines @@
       : error = null,
         isCached = false;
 
   BarbackServerResult._cached(this.url, this.id)
       : error = null,
         isCached = true;
 
   BarbackServerResult._failure(this.url, this.id, this.error)
       : isCached = false;
 }