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

sdk/lib/io/http.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.
 
 part of dart.io;
 
 /**
  * HTTP status codes.
  */
 abstract class HttpStatus {
@@ skipping 510 matching lines @@
    */
   factory HeaderValue([String value = "", Map<String, String> parameters]) {
     return new _HeaderValue(value, parameters);
   }
 
   /**
    * Creates a new header value object from parsing a header value
    * string with both value and optional parameters.
    */
   static HeaderValue parse(String value,
-                           {String parameterSeparator: ";"}) {
-    return _HeaderValue.parse(value, parameterSeparator: parameterSeparator);
+                           {String parameterSeparator: ";",
+                            bool preserveBackslash: false}) {
+    return _HeaderValue.parse(value,
+                              parameterSeparator: parameterSeparator,
+                              preserveBackslash: preserveBackslash);
   }
 
   /**
    * Gets the header value.
    */
   String get value;
 
   /**
    * Gets the map of parameters.
    *
@@ skipping 1051 matching lines @@
   final String message;
   final List<RedirectInfo> redirects;
 
   const RedirectException(String this.message,
                           List<RedirectInfo> this.redirects);
 
   String toString() => "RedirectException: $message";
 
   Uri get uri => redirects.last.location;
 }