Stop working around issue 2644.

pkg/http/lib/src/mock_client.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 mock_client;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'base_client.dart';
@@ skipping 20 matching lines @@
 
   /// Creates a [MockClient] with a handler that receives [Request]s and sends
   /// [Response]s.
   MockClient(MockClientHandler fn)
     : this._((baseRequest, bodyStream) {
       return bodyStream.toBytes().then((bodyBytes) {
         var request = new Request(baseRequest.method, baseRequest.url);
         request.persistentConnection = baseRequest.persistentConnection;
         request.followRedirects = baseRequest.followRedirects;
         request.maxRedirects = baseRequest.maxRedirects;
-        mapAddAll(request.headers, baseRequest.headers);
+        request.headers.addAll(baseRequest.headers);
         request.bodyBytes = bodyBytes;
         request.finalize();
 
         return fn(request);
       }).then((response) {
         return new StreamedResponse(
             new ByteStream.fromBytes(response.bodyBytes),
             response.statusCode,
             response.contentLength,
             request: baseRequest,
@@ skipping 29 matching lines @@
 }
 
 /// A handler function that receives [StreamedRequest]s and sends
 /// [StreamedResponse]s. Note that [request] will be finalized.
 typedef Future<StreamedResponse> MockClientStreamHandler(
     BaseRequest request, ByteStream bodyStream);
 
 /// A handler function that receives [Request]s and sends [Response]s. Note that
 /// [request] will be finalized.
 typedef Future<Response> MockClientHandler(Request request);