Add hint for amp-img. (#4483)
Add hint for amp-img. (#4483)

https://github.com/ampproject/amphtml/issues/4477
dotandads/amphtml,ecoron/amphtml,burtcorp/amphtml,rlugojr/amphtml,sebastianbenz/amphtml,cory-work/amphtml,zhouyx/amphtml,engtat/amphtml,Lith/amphtml,interspacejp/amphtml,taboola/amphtml,jlucero-contentad/amphtml,luciancrasovan/amphtml,luciancrasovan/amphtml,shawnbuso/amphtml,mlb7687/amphtml,BrightcoveOS/amphtml,ericlindley-g/amphtml,jasti/amphtml,zhucl/amphtml,kixer-com/amphtml,jmadler/amphtml,koshka/amphtml,bpaduch/amphtml,amoad-amoe/amphtml,mhc-gh/amphtml,adup-tech/amphtml,sriramkrish85/amphtml,prateekbh/amphtml,adtechnology/amphtml,comScore/amphtml,aghassemi/amphtml,bpaduch/amphtml,jridgewell/amphtml,engtat/amphtml,lannka/amphtml,rifler/amphtml,sortable/amphtml,arealit/amphtml,ampproject/amphtml,sortable/amphtml,nexxtv/amphtml,donttrustthisbot/amphtml,techhtml/amphtml,arealit/amphtml,sebastianbenz/amphtml,yieldmo/amphtml,Mobusi-ads/amphtml,criteo-forks/amphtml,jpettitt/amphtml,spotxchange/amphtml,gumgum/amphtml,techhtml/amphtml,kamtschatka/amphtml,Adtoma/amphtml,prateekbh/amphtml,dotandads/amphtml,Lith/amphtml,kmh287/amphtml,interspacejp/amphtml,mhc-gh/amphtml,yevheniiminin/amphtml,honeybadgerdontcare/amphtml,pedjoni8/amphtml,ADITION/amphtml,zhangsu/amphtml,koshka/amphtml,rsimha-amp/amphtml,triplelift/amphtml,voyagegroup/amphtml,alanorozco/amphtml,DarXector/amphtml,camelburrito/amphtml,Mixpo/amphtml,jlucero-contentad/amphtml,jmadler/amphtml,mhc-gh/amphtml,erwinmombay/amphtml,rsimha-amp/amphtml,yieldbot/amphtml,techhtml/amphtml,erwinmombay/amphtml,sharethrough/amphtml,kmh287/amphtml,comScore/amphtml,aghassemi/amphtml,cvializ/amphtml,BenDz/amphtml,cvializ/amphtml,prateekbh/amphtml,vmarteev/amphtml,BenDz/amphtml,mlb7687/amphtml,BrightcoveOS/amphtml,camelburrito/amphtml,JuliusThms/amphtml,engtat/amphtml,rlugojr/amphtml,interspacejp/amphtml,amoad-amoe/amphtml,avimehta/amphtml,Mixpo/amphtml,cory-work/amphtml,Adtoma/amphtml,spotxchange/amphtml,cory-work/amphtml,Gregable/amphtml,clawr/amphtml,Gregable/amphtml,AaronCritchley/amphtml,sklobovskaya/amphtml,pedjoni8/amphtml,arealit/amphtml,clawr/amphtml,jlucero-contentad/amphtml,burtcorp/amphtml,Gregable/amphtml,src-code/amphtml,sharethrough/amphtml,luciancrasovan/amphtml,zhucl/amphtml,danielrozenberg/amphtml,bpaduch/amphtml,britice/amphtml,rifler/amphtml,arealit/amphtml,tlong2/amphtml,ericlindley-g/amphtml,sharethrough/amphtml,media-net/amphtml,AaronCritchley/amphtml,dotandads/amphtml,yieldbot/amphtml,chaveznvg/amphtml,ampproject/amphtml,kamtschatka/amphtml,AaronCritchley/amphtml,DistroScale/amphtml,rajkumarsrk/amphtml,BrightcoveOS/amphtml,laterpay/amphtml,jridgewell/amphtml,lzanol/amphtml,jasti/amphtml,arealit/amphtml,DarXector/amphtml,burtcorp/amphtml,triplelift/amphtml,sortable/amphtml,vmarteev/amphtml,powdercloud/amphtml,media-net/amphtml,ecoron/amphtml,voyagegroup/amphtml,Lith/amphtml,chaveznvg/amphtml,tdrl/amphtml,jlucero-contentad/amphtml,techhtml/amphtml,sriramkrish85/amphtml,donttrustthisbot/amphtml,rlugojr/amphtml,dvoytenko/amphtml,ampproject/amphtml,sebastianbenz/amphtml,erwinmombay/amphtml,koshka/amphtml,keithwrightbos/amphtml,jdelhommeau/amphtml,bpaduch/amphtml,widespace-os/amphtml,honeybadgerdontcare/amphtml,zhucl/amphtml,ericlindley-g/amphtml,comScore/amphtml,BrightcoveOS/amphtml,pedjoni8/amphtml,clawr/amphtml,yieldmo/amphtml,AaronCritchley/amphtml,powdercloud/amphtml,devjsun/amphtml,smartadserver/amphtml,src-code/amphtml,media-net/amphtml,alanorozco/amphtml,triplelift/amphtml,luciancrasovan/amphtml,adtechnology/amphtml,engtat/amphtml,criteo-forks/amphtml,cvializ/amphtml,rajkumarsrk/amphtml,danielrozenberg/amphtml,chaveznvg/amphtml,clawr/amphtml,adiant/amphtml,jridgewell/amphtml,taboola/amphtml,zhucl/amphtml,jasti/amphtml,DarXector/amphtml,devjsun/amphtml,lzanol/amphtml,britice/amphtml,ecoron/amphtml,gumgum/amphtml,kixer-com/amphtml,lzanol/amphtml,prateekbh/amphtml,jlucero-contentad/amphtml,lzanol/amphtml,donttrustthisbot/amphtml,jdelhommeau/amphtml,chaveznvg/amphtml,BrightcoveOS/amphtml,prateekbh/amphtml,JuliusThms/amphtml,britice/amphtml,danielrozenberg/amphtml,zhouyx/amphtml,zhucl/amphtml,voyagegroup/amphtml,jmadler/amphtml,criteo-forks/amphtml,Adtoma/amphtml,rajkumarsrk/amphtml,jpettitt/amphtml,zhangsu/amphtml,zhangsu/amphtml,zhucl/amphtml,jasti/amphtml,ruturajv-media-net/amphtml,DistroScale/amphtml,tdrl/amphtml,koshka/amphtml,pietergreyling/amphtml,triplelift/amphtml,aghassemi/amphtml,engtat/amphtml,cvializ/amphtml,tdrl/amphtml,mlb7687/amphtml,jridgewell/amphtml,Gregable/amphtml,BenDz/amphtml,criteo-forks/amphtml,shawnbuso/amphtml,pedjoni8/amphtml,amoad-amoe/amphtml,laterpay/amphtml,adiant/amphtml,BrightcoveOS/amphtml,keithwrightbos/amphtml,adup-tech/amphtml,jmadler/amphtml,jpettitt/amphtml,ADITION/amphtml,koshka/amphtml,donttrustthisbot/amphtml,sortable/amphtml,danielrozenberg/amphtml,techhtml/amphtml,yieldbot/amphtml,kmh287/amphtml,ruturajv-media-net/amphtml,yevheniiminin/amphtml,rsimha-amp/amphtml,src-code/amphtml,Mobusi-ads/amphtml,DarXector/amphtml,cvializ/amphtml,laterpay/amphtml,ampproject/amphtml,pietergreyling/amphtml,jpettitt/amphtml,Lith/amphtml,keithwrightbos/amphtml,burtcorp/amphtml,Mixpo/amphtml,rifler/amphtml,src-code/amphtml,voyagegroup/amphtml,jmadler/amphtml,adiant/amphtml,chaveznvg/amphtml,taboola/amphtml,yandex-pcode/amphtml,adup-tech/amphtml,avimehta/amphtml,yevheniiminin/amphtml,donttrustthisbot/amphtml,zhangsu/amphtml,zhouyx/amphtml,dvoytenko/amphtml,keithwrightbos/amphtml,wjfang/amphtml,src-code/amphtml,smartadserver/amphtml,adiant/amphtml,camelburrito/amphtml,rajkumarsrk/amphtml,gumgum/amphtml,danielrozenberg/amphtml,adiant/amphtml,wjfang/amphtml,ecoron/amphtml,taboola/amphtml,clawr/amphtml,interspacejp/amphtml,sriramkrish85/amphtml,comScore/amphtml,rsimha-amp/amphtml,amoad-amoe/amphtml,ericlindley-g/amphtml,AaronCritchley/amphtml,kixer-com/amphtml,media-net/amphtml,Mobusi-ads/amphtml,dvoytenko/amphtml,dotandads/amphtml,kixer-com/amphtml,JuliusThms/amphtml,lzanol/amphtml,media-net/amphtml,Gregable/amphtml,erwinmombay/amphtml,criteo-forks/amphtml,rajkumarsrk/amphtml,burtcorp/amphtml,amoad-amoe/amphtml,Mixpo/amphtml,adtechnology/amphtml,jpettitt/amphtml,kixer-com/amphtml,camelburrito/amphtml,mlb7687/amphtml,sklobovskaya/amphtml,kixer-com/amphtml,DAC-f1h-dev/amphtml,pietergreyling/amphtml,spotxchange/amphtml,fullspeed-sp/amphtml,DistroScale/amphtml,ampproject/amphtml,dotandads/amphtml,koshka/amphtml,tdrl/amphtml,danielrozenberg/amphtml,yandex-pcode/amphtml,jridgewell/amphtml,lannka/amphtml,yevheniiminin/amphtml,smartadserver/amphtml,kmh287/amphtml,taboola/amphtml,gumgum/amphtml,voyagegroup/amphtml,jpettitt/amphtml,pietergreyling/amphtml,shawnbuso/amphtml,tlong2/amphtml,jasti/amphtml,jpettitt/amphtml,ADITION/amphtml,gumgum/amphtml,vmarteev/amphtml,fullspeed-sp/amphtml,yieldmo/amphtml,powdercloud/amphtml,triplelift/amphtml,mhc-gh/amphtml,yevheniiminin/amphtml,interspacejp/amphtml,kmh287/amphtml,clawr/amphtml,jlucero-contentad/amphtml,honeybadgerdontcare/amphtml,adup-tech/amphtml,wjfang/amphtml,BenDz/amphtml,shawnbuso/amphtml,adiant/amphtml,smartadserver/amphtml,widespace-os/amphtml,zhouyx/amphtml,honeybadgerdontcare/amphtml,yandex-pcode/amphtml,fullspeed-sp/amphtml,vmarteev/amphtml,tlong2/amphtml,vmarteev/amphtml,dotandads/amphtml,vmarteev/amphtml,jdelhommeau/amphtml,ruturajv-media-net/amphtml,sriramkrish85/amphtml,spotxchange/amphtml,adtechnology/amphtml,yieldmo/amphtml,arealit/amphtml,ecoron/amphtml,wjfang/amphtml,lannka/amphtml,adiant/amphtml,kamtschatka/amphtml,BenDz/amphtml,donttrustthisbot/amphtml,cvializ/amphtml,dvoytenko/amphtml,JuliusThms/amphtml,chaveznvg/amphtml,lannka/amphtml,camelburrito/amphtml,tlong2/amphtml,src-code/amphtml,ecoron/amphtml,lannka/amphtml,danielrozenberg/amphtml,DistroScale/amphtml,adtechnology/amphtml,jdelhommeau/amphtml,mhc-gh/amphtml,Mixpo/amphtml,JuliusThms/amphtml,yevheniiminin/amphtml,powdercloud/amphtml,prateekbh/amphtml,arealit/amphtml,lannka/amphtml,yieldbot/amphtml,rajkumarsrk/amphtml,aghassemi/amphtml,adup-tech/amphtml,sortable/amphtml,fullspeed-sp/amphtml,fullspeed-sp/amphtml,tdrl/amphtml,zhangsu/amphtml,nexxtv/amphtml,Adtoma/amphtml,mhc-gh/amphtml,honeybadgerdontcare/amphtml,adup-tech/amphtml,lannka/amphtml,luciancrasovan/amphtml,nexxtv/amphtml,spotxchange/amphtml,honeybadgerdontcare/amphtml,aghassemi/amphtml,bpaduch/amphtml,mhc-gh/amphtml,erwinmombay/amphtml,mlb7687/amphtml,Mobusi-ads/amphtml,sriramkrish85/amphtml,comScore/amphtml,techhtml/amphtml,widespace-os/amphtml,donttrustthisbot/amphtml,laterpay/amphtml,fullspeed-sp/amphtml,pedjoni8/amphtml,Mobusi-ads/amphtml,rsimha-amp/amphtml,spotxchange/amphtml,dvoytenko/amphtml,jdelhommeau/amphtml,alanorozco/amphtml,ericlindley-g/amphtml,powdercloud/amphtml,sharethrough/amphtml,camelburrito/amphtml,cory-work/amphtml,DAC-f1h-dev/amphtml,DistroScale/amphtml,devjsun/amphtml,kamtschatka/amphtml,alanorozco/amphtml,alanorozco/amphtml,BenDz/amphtml,kamtschatka/amphtml,shawnbuso/amphtml,pietergreyling/amphtml,rlugojr/amphtml,triplelift/amphtml,britice/amphtml,powdercloud/amphtml,sriramkrish85/amphtml,smartadserver/amphtml,sebastianbenz/amphtml,ruturajv-media-net/amphtml,nexxtv/amphtml,kamtschatka/amphtml,rsimha-amp/amphtml,cory-work/amphtml,luciancrasovan/amphtml,pietergreyling/amphtml,ruturajv-media-net/amphtml,danielrozenberg/amphtml,yandex-pcode/amphtml,Gregable/amphtml,avimehta/amphtml,cory-work/amphtml,sebastianbenz/amphtml,bpaduch/amphtml,Mixpo/amphtml,zhangsu/amphtml,DarXector/amphtml,yieldbot/amphtml,erwinmombay/amphtml,keithwrightbos/amphtml,prateekbh/amphtml,lzanol/amphtml,DAC-f1h-dev/amphtml,pedjoni8/amphtml,avimehta/amphtml,comScore/amphtml,alanorozco/amphtml,alanorozco/amphtml,ADITION/amphtml,rifler/amphtml,devjsun/amphtml,yieldmo/amphtml,shawnbuso/amphtml,Gregable/amphtml,kmh287/amphtml,devjsun/amphtml,Mobusi-ads/amphtml,wjfang/amphtml,tdrl/amphtml,jpettitt/amphtml,engtat/amphtml,taboola/amphtml,JuliusThms/amphtml,sklobovskaya/amphtml,jridgewell/amphtml,jmadler/amphtml,zhouyx/amphtml,AaronCritchley/amphtml,rifler/amphtml,sklobovskaya/amphtml,smartadserver/amphtml,yandex-pcode/amphtml,DAC-f1h-dev/amphtml,sortable/amphtml,ericlindley-g/amphtml,Adtoma/amphtml,rsimha-amp/amphtml,amoad-amoe/amphtml,laterpay/amphtml,tlong2/amphtml,voyagegroup/amphtml,yieldbot/amphtml,taboola/amphtml,comScore/amphtml,mhc-gh/amphtml,yieldmo/amphtml,sklobovskaya/amphtml,keithwrightbos/amphtml,gumgum/amphtml,camelburrito/amphtml,yandex-pcode/amphtml,jdelhommeau/amphtml,media-net/amphtml,dvoytenko/amphtml,luciancrasovan/amphtml,gumgum/amphtml,mlb7687/amphtml,devjsun/amphtml,yieldmo/amphtml,Gregable/amphtml,powdercloud/amphtml,DAC-f1h-dev/amphtml,sebastianbenz/amphtml,rajkumarsrk/amphtml,nexxtv/amphtml,widespace-os/amphtml,sharethrough/amphtml,widespace-os/amphtml,sharethrough/amphtml,ampproject/amphtml,jridgewell/amphtml,aghassemi/amphtml,sklobovskaya/amphtml,ruturajv-media-net/amphtml,DarXector/amphtml,nexxtv/amphtml,interspacejp/amphtml,Lith/amphtml,tlong2/amphtml,rlugojr/amphtml,media-net/amphtml,ampproject/amphtml,laterpay/amphtml,DAC-f1h-dev/amphtml,alanorozco/amphtml,clawr/amphtml,vmarteev/amphtml,honeybadgerdontcare/amphtml,criteo-forks/amphtml,adtechnology/amphtml,zhucl/amphtml,cory-work/amphtml,jasti/amphtml,avimehta/amphtml,zhouyx/amphtml,engtat/amphtml,bpaduch/amphtml,wjfang/amphtml,rlugojr/amphtml,nexxtv/amphtml,sklobovskaya/amphtml,burtcorp/amphtml,widespace-os/amphtml,ADITION/amphtml,DistroScale/amphtml,shawnbuso/amphtml,kixer-com/amphtml,rifler/amphtml,zhouyx/amphtml,keithwrightbos/amphtml,ampproject/amphtml,wjfang/amphtml,voyagegroup/amphtml,yandex-pcode/amphtml,Lith/amphtml,avimehta/amphtml,media-net/amphtml,Adtoma/amphtml