We need to support passing optional filename when FormData.append() is used to append a blob, per the latest XHR 2 spec:
When the append(name, value, filename) method is invoked, the user agent must create a new entry with the following parameters set and append it to the end of the collection the FormData object represents:
Set its name to name.
Set its value to value.
Set its type to "text" if value is a string and "file" if it is a Blob.
If its type is "file" set its filename to "blob".
If its type is "file" and value is a File whose name attribute is not the empty string, set entry's filename to the attribute's value.
If the filename parameter is not omitted set entry's filename to filename.
Created attachment 110614 [details]
Attachment 110614 [details] did not pass style-queue:
Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'LayoutTests/ChangeLog', u'LayoutTests/http..." exit_code: 1
LayoutTests/ChangeLog:1: ChangeLog entry has no bug number [changelog/bugnumber] 
Total errors found: 1 in 13 files
If any of these errors are false positives, please file a bug against check-webkit-style.
Created attachment 110616 [details]
Comment on attachment 110616 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=110616&action=review
Please consider adding that test.
> + filename = toWebCoreStringWithNullCheck(args);
It would be nice to add a test with null as the last arg. It looks like you added handling throughout the code for this but it seems untested.
New test case added to cover null argument case.
Committed as http://trac.webkit.org/changeset/97274.