The panels created via extensions API appear truncated, because iframes created to host the panels use default height. The height needs to be set to 100%.
Created attachment 64696 [details] patch
Comment on attachment 64696 [details] patch Clearing flags on attachment: 64696 Committed r65607: <http://trac.webkit.org/changeset/65607>
All reviewed patches have been landed. Closing bug.