This parameter was added in r63864. Right now it is simply unused.
Created attachment 66826 [details] Patch for this issue
Comment on attachment 66826 [details] Patch for this issue View in context: https://bugs.webkit.org/attachment.cgi?id=66826&action=prettypatch LGTM. Can you explain a bit more in the changeLog what you are doing? I think the headline of the bug is not explicit enough. r=me with more details in the ChangeLog.
Committed r66983: <http://trac.webkit.org/changeset/66983>