Preserve '\' in filenames for uploads, as Windows/IE contains them.

pkg/http_server/test/http_multipart_test.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 "package:http_server/http_server.dart";
 import "package:mime/mime.dart";
 import "package:unittest/unittest.dart";
 import 'dart:async';
 import 'dart:io';
 import 'dart:convert';
@@ skipping 88 matching lines @@
 Content-Disposition: form-data; name="submit-name"\r
 \r
 Larry\r
 --AaB03x\r
 Content-Disposition: form-data; name="files"; filename="file1.txt"\r
 Content-Type: text/plain\r
 \r
 Content of file\r
 --AaB03x--\r\n''';
 
-
   postDataTest(message.codeUnits,
                'multipart/form-data',
                'AaB03x',
                [new FormField('submit-name', 'Larry'),
                 new FormField('files',
                               'Content of file',
                               contentType: 'text/plain',
                               filename: 'file1.txt')]);
+
+  // Windows/IE style file upload.
+  message = '''
+\r\n--AaB03x\r
+Content-Disposition: form-data; name="files"; filename="C:\\file1\\".txt"\r
+Content-Type: text/plain\r
+\r
+Content of file\r
+--AaB03x--\r\n''';
+
+
+  postDataTest(message.codeUnits,
+               'multipart/form-data',
+               'AaB03x',
+               [new FormField('files',
+                              'Content of file',
+                              contentType: 'text/plain',
+                              filename: 'C:\\file1".txt')]);
   // Similar test using Chrome posting.
   message = [
       45, 45, 45, 45, 45, 45, 87, 101, 98, 75, 105, 116, 70, 111, 114, 109, 66,
       111, 117, 110, 100, 97, 114, 121, 81, 83, 113, 108, 56, 107, 68, 65, 76,
       77, 55, 116, 65, 107, 67, 49, 13, 10, 67, 111, 110, 116, 101, 110, 116,
       45, 68, 105, 115, 112, 111, 115, 105, 116, 105, 111, 110, 58, 32, 102,
       111, 114, 109, 45, 100, 97, 116, 97, 59, 32, 110, 97, 109, 101, 61, 34,
       115, 117, 98, 109, 105, 116, 45, 110, 97, 109, 101, 34, 13, 10, 13, 10,
       84, 101, 115, 116, 13, 10, 45, 45, 45, 45, 45, 45, 87, 101, 98, 75, 105,
       116, 70, 111, 114, 109, 66, 111, 117, 110, 100, 97, 114, 121, 81, 83, 113,
@@ skipping 62 matching lines @@
   postDataTest(message,
                'multipart/form-data',
                '----WebKitFormBoundaryfe0EzV1aNysD1bPh',
                [new FormField('name', 'øv')]);
 }
 
 
 void main() {
   testPostData();
 }