Fix tests for VM in checked mode.

pkg/http/test/client_test.dart

 // Copyright (c) 2012, 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 client_test;
 
 import 'dart:io';
 
 import 'package:unittest/unittest.dart';
 import 'package:http/http.dart' as http;
@@ skipping 10 matching lines @@
     request.headers[HttpHeaders.CONTENT_TYPE] =
       'application/json; charset=utf-8';
 
     var future = client.send(request).then((response) {
       expect(response.request, equals(request));
       expect(response.statusCode, equals(200));
       return consumeInputStream(response.stream);
     }).then((bytes) => new String.fromCharCodes(bytes));
     future.catchError((_) {}).then((_) => client.close());
 
-    expect(future, completion(parse(equals({
-      'method': 'POST',
-      'path': '/',
-      'headers': {
-        'content-type': ['application/json; charset=utf-8'],
-        'transfer-encoding': ['chunked']
-      },
-      'body': '{"hello": "world"}'
-    }))));
+    future.then(expectAsync1((content) {
+      expect(content, parse(equals({
+        'method': 'POST',
+        'path': '/',
+        'headers': {
+          'content-type': ['application/json; charset=utf-8'],
+          'transfer-encoding': ['chunked']
+        },
+        'body': '{"hello": "world"}'
+      })));
+    }));
 
     request.stream.writeString('{"hello": "world"}');
     request.stream.close();
   });
 }