Fix test-iframe-createIframeWithMessageStub failures on older browsers (#5895)
Fix test-iframe-createIframeWithMessageStub failures on older browsers (#5895)


lzanol/amphtml,wjfang/amphtml,danielrozenberg/amphtml,wjfang/amphtml,erwinmombay/amphtml,rsimha-amp/amphtml,yandex-pcode/amphtml,lannka/amphtml,clawr/amphtml,taboola/amphtml,voyagegroup/amphtml,DarXector/amphtml,engtat/amphtml,kamtschatka/amphtml,jdelhommeau/amphtml,rlugojr/amphtml,clawr/amphtml,voyagegroup/amphtml,pedjoni8/amphtml,laterpay/amphtml,Adtoma/amphtml,jmadler/amphtml,ruturajv-media-net/amphtml,pedjoni8/amphtml,tlong2/amphtml,aghassemi/amphtml,avimehta/amphtml,lannka/amphtml,gumgum/amphtml,smartadserver/amphtml,widespace-os/amphtml,prateekbh/amphtml,triplelift/amphtml,sharethrough/amphtml,luciancrasovan/amphtml,gumgum/amphtml,yieldmo/amphtml,ecoron/amphtml,arealit/amphtml,sebastianbenz/amphtml,ecoron/amphtml,rifler/amphtml,fullspeed-sp/amphtml,media-net/amphtml,yandex-pcode/amphtml,BenDz/amphtml,sharethrough/amphtml,taboola/amphtml,kixer-com/amphtml,ADITION/amphtml,widespace-os/amphtml,ampproject/amphtml,powdercloud/amphtml,burtcorp/amphtml,ruturajv-media-net/amphtml,luciancrasovan/amphtml,dotandads/amphtml,wjfang/amphtml,donttrustthisbot/amphtml,yieldbot/amphtml,wjfang/amphtml,yieldbot/amphtml,spotxchange/amphtml,rlugojr/amphtml,fullspeed-sp/amphtml,src-code/amphtml,zhouyx/amphtml,ruturajv-media-net/amphtml,zhangsu/amphtml,alanorozco/amphtml,DarXector/amphtml,rifler/amphtml,cvializ/amphtml,jlucero-contentad/amphtml,zhucl/amphtml,nexxtv/amphtml,pedjoni8/amphtml,lannka/amphtml,cvializ/amphtml,rajkumarsrk/amphtml,jridgewell/amphtml,pietergreyling/amphtml,DAC-f1h-dev/amphtml,JuliusThms/amphtml,jpettitt/amphtml,media-net/amphtml,avimehta/amphtml,jlucero-contentad/amphtml,comScore/amphtml,burtcorp/amphtml,vmarteev/amphtml,techhtml/amphtml,gumgum/amphtml,lzanol/amphtml,dotandads/amphtml,sklobovskaya/amphtml,gumgum/amphtml,sklobovskaya/amphtml,rajkumarsrk/amphtml,donttrustthisbot/amphtml,tdrl/amphtml,yandex-pcode/amphtml,Gregable/amphtml,camelburrito/amphtml,adup-tech/amphtml,zhangsu/amphtml,jpettitt/amphtml,jlucero-contentad/amphtml,aghassemi/amphtml,yieldmo/amphtml,techhtml/amphtml,honeybadgerdontcare/amphtml,jridgewell/amphtml,src-code/amphtml,prateekbh/amphtml,adiant/amphtml,DistroScale/amphtml,jdelhommeau/amphtml,adiant/amphtml,yieldmo/amphtml,jridgewell/amphtml,koshka/amphtml,ampproject/amphtml,smartadserver/amphtml,widespace-os/amphtml,avimehta/amphtml,jdelhommeau/amphtml,yandex-pcode/amphtml,dotandads/amphtml,pietergreyling/amphtml,zhucl/amphtml,widespace-os/amphtml,mlb7687/amphtml,DistroScale/amphtml,Gregable/amphtml,kixer-com/amphtml,Mobusi-ads/amphtml,camelburrito/amphtml,ruturajv-media-net/amphtml,arealit/amphtml,zhouyx/amphtml,ampproject/amphtml,lannka/amphtml,honeybadgerdontcare/amphtml,tlong2/amphtml,techhtml/amphtml,yieldmo/amphtml,koshka/amphtml,sebastianbenz/amphtml,koshka/amphtml,rlugojr/amphtml,ecoron/amphtml,DarXector/amphtml,burtcorp/amphtml,keithwrightbos/amphtml,yandex-pcode/amphtml,kixer-com/amphtml,DarXector/amphtml,src-code/amphtml,engtat/amphtml,widespace-os/amphtml,danielrozenberg/amphtml,kmh287/amphtml,BenDz/amphtml,ampproject/amphtml,sebastianbenz/amphtml,arealit/amphtml,adup-tech/amphtml,media-net/amphtml,lzanol/amphtml,jpettitt/amphtml,mhc-gh/amphtml,sharethrough/amphtml,mlb7687/amphtml,shawnbuso/amphtml,sklobovskaya/amphtml,bpaduch/amphtml,comScore/amphtml,ADITION/amphtml,bpaduch/amphtml,jridgewell/amphtml,cory-work/amphtml,engtat/amphtml,kamtschatka/amphtml,pedjoni8/amphtml,Gregable/amphtml,ADITION/amphtml,interspacejp/amphtml,clawr/amphtml,sklobovskaya/amphtml,JuliusThms/amphtml,zhouyx/amphtml,sortable/amphtml,sortable/amphtml,kamtschatka/amphtml,mlb7687/amphtml,Adtoma/amphtml,sklobovskaya/amphtml,Adtoma/amphtml,laterpay/amphtml,ampproject/amphtml,taboola/amphtml,jmadler/amphtml,sharethrough/amphtml,sebastianbenz/amphtml,cory-work/amphtml,burtcorp/amphtml,DAC-f1h-dev/amphtml,mlb7687/amphtml,DarXector/amphtml,prateekbh/amphtml,spotxchange/amphtml,sklobovskaya/amphtml,Mobusi-ads/amphtml,chaveznvg/amphtml,yieldmo/amphtml,widespace-os/amphtml,laterpay/amphtml,interspacejp/amphtml,keithwrightbos/amphtml,dotandads/amphtml,yieldbot/amphtml,rifler/amphtml,lannka/amphtml,cvializ/amphtml,koshka/amphtml,pietergreyling/amphtml,tdrl/amphtml,mhc-gh/amphtml,nexxtv/amphtml,sortable/amphtml,cory-work/amphtml,fullspeed-sp/amphtml,yieldbot/amphtml,nexxtv/amphtml,cory-work/amphtml,DarXector/amphtml,Adtoma/amphtml,jdelhommeau/amphtml,Mobusi-ads/amphtml,comScore/amphtml,kixer-com/amphtml,adup-tech/amphtml,bpaduch/amphtml,rsimha-amp/amphtml,prateekbh/amphtml,voyagegroup/amphtml,zhouyx/amphtml,DistroScale/amphtml,adup-tech/amphtml,clawr/amphtml,vmarteev/amphtml,zhangsu/amphtml,cory-work/amphtml,mhc-gh/amphtml,tdrl/amphtml,ecoron/amphtml,interspacejp/amphtml,alanorozco/amphtml,Gregable/amphtml,comScore/amphtml,rifler/amphtml,tdrl/amphtml,engtat/amphtml,BenDz/amphtml,sriramkrish85/amphtml,jridgewell/amphtml,luciancrasovan/amphtml,lannka/amphtml,DistroScale/amphtml,avimehta/amphtml,sharethrough/amphtml,rsimha-amp/amphtml,jlucero-contentad/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,triplel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amphtml,alanorozco/amphtml,arealit/amphtml,camelburrito/amphtml,tlong2/amphtml,erwinmombay/amphtml