Add a simple iframe test harness to play with during development.
Add a simple iframe test harness to play with during development.

borgified/vimium,crazypenguincode/vimium,willsALMANJ/vimium,dimatter/vimium,PickRelated/vimium,poacher2k/vimium,csmalin/vimium,VPashkov/vimium,justalittlenoob/vimium,csmalin/vimium,bkudria/vimium,bkudria/vimium,elderbas/vimium,hhsue/vimium,Robinson10240/vimium,Robinson10240/vimium,borgified/vimium,elegantwww/vimium,csmalin/vimium,gdh1995/vimium,decaffeinate-examples/vimium,poacher2k/vimium,gdh1995/vimium,zhangmin510/vimium,elegantwww/vimium,smblott-github/vimium-smblott,smblott-github/vimium,Lw-Cui/vimium,tuchangwei/vimium,jb55/vimium-plus,justalittlenoob/vimium,PickRelated/vimium,VPashkov/vimium,Aleroniponi/vimium,justalittlenoob/vimium,llimllib/vimium,douglas-larocca/vimium,jb55/vimium-plus,Aleroniponi/vimium,douglas-larocca/vimium,crazypenguincode/vimium,smblott-github/vimium-smblott,Aleroniponi/vimium,wildeyes/vimium,philc/vimium,gdh1995/vimium,hhsue/vimium,Robinson10240/vimium,PrestanceDesign/vimium,VPashkov/vimium,cyrixhero/vimium,zhangmin510/vimium,zhangmin510/vimium,philc/vimium,mrmr1993/vimium,Lw-Cui/vimium,dimatter/vimium,dimatter/vimium,wildeyes/vimium,willsALMANJ/vimium,PickRelated/vimium,PrestanceDesign/vimium,shaung/vimium,mrmr1993/vimium,elderbas/vimium,mrmr1993/vimium,smblott-github/vimium,decaffeinate-examples/vimium,cyrixhero/vimium,willsALMANJ/vimium,poacher2k/vimium,elegantwww/vimium,PrestanceDesign/vimium,cyrixhero/vimium,tuchangwei/vimium,elderbas/vimium,smblott-github/vimium,borgified/vimium,wildeyes/vimium,hhsue/vimium,decaffeinate-examples/vimium,bkudria/vimium,Lw-Cui/vimium,tuchangwei/vimium,philc/vimium,douglas-larocca/vimium