Update pkg/http to use the new async APIs.

pkg/http/lib/http.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.
 
 /// A composable, [Future]-based library for making HTTP requests.
 ///
 /// The easiest way to use this library is via the top-level functions. They
 /// allow you to make individual HTTP requests with minimal hassle:
 ///
 ///     import 'package:http/http.dart' as http;
@@ skipping 10 matching lines @@
 /// If you're making multiple requests to the same server, you can keep open a
 /// persistent connection by using a [Client] rather than making one-off
 /// requests. If you do this, make sure to close the client when you're done:
 ///
 ///     var client = new http.Client();
 ///     client.post(
 ///         "http://example.com/whatsit/create",
 ///         fields: {"name": "doodle", "color": "blue"})
 ///       .then((response) => client.get(response.bodyFields['uri']))
 ///       .then((response) => print(response.body))
-///       .onComplete((_) => client.close());
+///       .whenComplete(client.close);
 ///
 /// You can also exert more fine-grained control over your requests and
 /// responses by creating [Request] or [StreamedRequest] objects yourself and
 /// passing them to [Client.send].
 ///
 /// This package is designed to be composable. This makes it easy for external
 /// libraries to work with one another to add behavior to it. Libraries wishing
 /// to add behavior should create a subclass of [BaseClient] that wraps another
 /// [Client] and adds the desired behavior:
 ///
@@ skipping 14 matching lines @@
 import 'dart:async';
 import 'dart:scalarlist';
 import 'dart:uri';
 
 import 'src/client.dart';
 import 'src/response.dart';
 
 export 'src/base_client.dart';
 export 'src/base_request.dart';
 export 'src/base_response.dart';
+export 'src/byte_stream.dart';
 export 'src/client.dart';
 export 'src/multipart_file.dart';
 export 'src/multipart_request.dart';
 export 'src/request.dart';
 export 'src/response.dart';
 export 'src/streamed_request.dart';
 export 'src/streamed_response.dart';
 
 /// Sends an HTTP HEAD request with the given headers to the given URL, which
 /// can be a [Uri] or a [String].
@@ skipping 86 matching lines @@
 /// the same server, you should use a single [Client] for all of those requests.
 ///
 /// For more fine-grained control over the request and response, use [Request]
 /// instead.
 Future<Uint8List> readBytes(url, {Map<String, String> headers}) =>
   _withClient((client) => client.readBytes(url, headers: headers));
 
 Future _withClient(Future fn(Client)) {
   var client = new Client();
   var future = fn(client);
-  future.catchError((_) {}).then((_) => client.close());
-  return future;
+  return future.whenComplete(client.close);
 }