Pass Redirect status higher than 307 through to the user

tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate

 // 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.
 
 part of $LIBRARYNAME;
 
  /**
   * A client-side XHR request for getting data from a URL,
   * formally known as XMLHttpRequest.
   *
@@ skipping 203 matching lines @@
       requestHeaders.forEach((header, value) {
         xhr.setRequestHeader(header, value);
       });
     }
 
     if (onProgress != null) {
       xhr.onProgress.listen(onProgress);
     }
 
     xhr.onLoad.listen((e) {
-      // Note: file:// URIs have status of 0.
-      if ((xhr.status >= 200 && xhr.status < 300) ||
-          xhr.status == 0 || xhr.status == 304) {
+      var accepted = xhr.status >= 200 && xhr.status < 300;
+      var fileUri = xhr.status == 0; // file:// URIs have status of 0.
+      var notModified = xhr.status == 304;
+      // Redirect status is specified up to 307, but others have been used in
+      // practice. Notably Google Drive uses 308 Resume Incomplete for
+      // resumable uploads, and it's also been used as a redirect. The
+      // redirect case will be handled by the browser before it gets to us,
+      // so if we see it we should pass it through to the user.
+      var unknownRedirect = xhr.status > 307 && xhr.status < 400;
+      
+      if (accepted || fileUri || notModified || unknownRedirect) {
         completer.complete(xhr);
       } else {
         completer.completeError(e);
       }
     });
 
     xhr.onError.listen(completer.completeError);
 
     if (sendData != null) {
       xhr.send(sendData);
@@ skipping 134 matching lines @@
         headers[key] = '${headers[key]}, $value';
       } else {
         headers[key] = value;
       }
     }
     return headers;
   }
 
 $!MEMBERS
 }