HTML5 no longer says that top-level frame application cache should be used for child frames. I'm not sure if I know all the reasons for this, but security is certainly one - otherwise, a different origin subframe could add dynamic entries to the main thread's cache.
Created attachment 26247 [details] proposed fix
s/main thread's/top frame's/ :)
Comment on attachment 26247 [details] proposed fix r=me
Committed <http://trac.webkit.org/changeset/39474>.