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

pkg/http_server/test/http_multipart_test.dart

Index: pkg/http_server/test/http_multipart_test.dart
diff --git a/pkg/http_server/test/http_multipart_test.dart b/pkg/http_server/test/http_multipart_test.dart
index 10d695b15801c7e1ff27089e8e2a079418d3e255..d1d08434fcaa0c915e93550c34d42dce9e5ecb28 100644
--- a/pkg/http_server/test/http_multipart_test.dart
+++ b/pkg/http_server/test/http_multipart_test.dart
@@ -106,7 +106,6 @@ Content-Type: text/plain\r
 Content of file\r
 --AaB03x--\r\n''';
 
-
   postDataTest(message.codeUnits,
                'multipart/form-data',
                'AaB03x',
@@ -115,6 +114,24 @@ Content of file\r
                               '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,