It's from blackberry internal bug#149283 to support byte-range download.
Created attachment 143950 [details] Patch
Comment on attachment 143950 [details] Patch Looks good.
Comment on attachment 143950 [details] Patch Clearing flags on attachment: 143950 Committed r118526: <http://trac.webkit.org/changeset/118526>
All reviewed patches have been landed. Closing bug.