Add support for HttpServer.defaultResponseHeaders to HttpMultiServer.

pkg/http_multi_server/test/http_multi_server_test.dart

 // Copyright (c) 2014, 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 http_multi_server.test;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:http/http.dart' as http;
@@ skipping 42 matching lines @@
 
       expect(_get(subServer2).then((response) {
         expect(response.headers['server'], equals("http_multi_server test"));
       }), completes);
 
       expect(_get(subServer3).then((response) {
         expect(response.headers['server'], equals("http_multi_server test"));
       }), completes);
     });
 
+    test("headers.set sets the value for all servers", () {
+      multiServer.defaultResponseHeaders.set(
+          "server", "http_multi_server test");
+
+      multiServer.listen((request) {
+        request.response.write("got request");
+        request.response.close();
+      });
+
+      expect(_get(subServer1).then((response) {
+        expect(response.headers['server'], equals("http_multi_server test"));
+      }), completes);
+
+      expect(_get(subServer2).then((response) {
+        expect(response.headers['server'], equals("http_multi_server test"));
+      }), completes);
+
+      expect(_get(subServer3).then((response) {
+        expect(response.headers['server'], equals("http_multi_server test"));
+      }), completes);
+    });
+
     test("connectionsInfo sums the values for all servers", () {
       var pendingRequests = 0;
       var awaitingResponseCompleter = new Completer();
       var sendResponseCompleter = new Completer();
       multiServer.listen((request) {
         sendResponseCompleter.future.then((_) {
           request.response.write("got request");
           request.response.close();
         });
 
@@ skipping 46 matching lines @@
 
 /// Makes a GET request to the root of [server] and returns the response.
 Future<http.Response> _get(HttpServer server) => http.get(_urlFor(server));
 
 /// Makes a GET request to the root of [server] and returns the response body.
 Future<String> _read(HttpServer server) => http.read(_urlFor(server));
 
 /// Returns the URL for the root of [server].
 String _urlFor(HttpServer server) =>
     "http://${server.address.host}:${server.port}/";