Ensure frames is defined.
Ensure frames is defined.

When we reinject content scripts into a tab where document.body is a
frameset, no frames are registered, which causes frames to be undefined.

elegantwww/vimium,borgified/vimium,bkudria/vimium,wildeyes/vimium,poacher2k/vimium,tuchangwei/vimium,VPashkov/vimium,elderbas/vimium,justalittlenoob/vimium,cyrixhero/vimium,mrmr1993/vimium,Lw-Cui/vimium,gdh1995/vimium,philc/vimium,Robinson10240/vimium,smblott-github/vimium,zhangmin510/vimium,smblott-github/vimium,borgified/vimium,douglas-larocca/vimium,Lw-Cui/vimium,willsALMANJ/vimium,csmalin/vimium,PickRelated/vimium,Aleroniponi/vimium,PrestanceDesign/vimium,tuchangwei/vimium,dimatter/vimium,douglas-larocca/vimium,VPashkov/vimium,dimatter/vimium,poacher2k/vimium,smblott-github/vimium,elderbas/vimium,Aleroniponi/vimium,douglas-larocca/vimium,PickRelated/vimium,bkudria/vimium,mrmr1993/vimium,gdh1995/vimium,gdh1995/vimium,philc/vimium,hhsue/vimium,PrestanceDesign/vimium,justalittlenoob/vimium,wildeyes/vimium,Lw-Cui/vimium,elegantwww/vimium,PickRelated/vimium,csmalin/vimium,willsALMANJ/vimium,Aleroniponi/vimium,hhsue/vimium,elegantwww/vimium,elderbas/vimium,justalittlenoob/vimium,borgified/vimium,zhangmin510/vimium,tuchangwei/vimium,bkudria/vimium,mrmr1993/vimium,willsALMANJ/vimium,dimatter/vimium,cyrixhero/vimium,wildeyes/vimium,zhangmin510/vimium,hhsue/vimium,decaffeinate-examples/vimium,PrestanceDesign/vimium,decaffeinate-examples/vimium,decaffeinate-examples/vimium,philc/vimium,poacher2k/vimium,Robinson10240/vimium,csmalin/vimium,VPashkov/vimium,cyrixhero/vimium,Robinson10240/vimium