xhr: Minor test improvements (#26933)
xhr: Minor test improvements (#26933)

Expect console errors.
zhouyx/amphtml,honeybadgerdontcare/amphtml,alanorozco/amphtml,taboola/amphtml,rsimha-amp/amphtml,honeybadgerdontcare/amphtml,mhc-gh/amphtml,media-net/amphtml,yandex-pcode/amphtml,nexxtv/amphtml,alanorozco/amphtml,ampproject/amphtml,jpettitt/amphtml,sharethrough/amphtml,mhc-gh/amphtml,lannka/amphtml,media-net/amphtml,yandex-pcode/amphtml,adup-tech/amphtml,yandex-pcode/amphtml,nexxtv/amphtml,sharethrough/amphtml,lannka/amphtml,cory-work/amphtml,smartadserver/amphtml,danielrozenberg/amphtml,nexxtv/amphtml,zhouyx/amphtml,voyagegroup/amphtml,lannka/amphtml,alanorozco/amphtml,jridgewell/amphtml,Gregable/amphtml,lannka/amphtml,honeybadgerdontcare/amphtml,jridgewell/amphtml,taboola/amphtml,jpettitt/amphtml,prateekbh/amphtml,voyagegroup/amphtml,adup-tech/amphtml,zhouyx/amphtml,mhc-gh/amphtml,taboola/amphtml,lannka/amphtml,voyagegroup/amphtml,taboola/amphtml,ampproject/amphtml,rsimha-amp/amphtml,danielrozenberg/amphtml,sharethrough/amphtml,ampproject/amphtml,mhc-gh/amphtml,ampproject/amphtml,alanorozco/amphtml,jmadler/amphtml,cory-work/amphtml,alanorozco/amphtml,nexxtv/amphtml,prateekbh/amphtml,jpettitt/amphtml,jmadler/amphtml,zhouyx/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,cory-work/amphtml,alanorozco/amphtml,jridgewell/amphtml,alanorozco/amphtml,Gregable/amphtml,adup-tech/amphtml,lannka/amphtml,prateekbh/amphtml,rsimha-amp/amphtml,adup-tech/amphtml,media-net/amphtml,danielrozenberg/amphtml,sharethrough/amphtml,zhouyx/amphtml,honeybadgerdontcare/amphtml,zhouyx/amphtml,danielrozenberg/amphtml,ampproject/amphtml,jridgewell/amphtml,voyagegroup/amphtml,cory-work/amphtml,rsimha-amp/amphtml,sharethrough/amphtml,prateekbh/amphtml,jridgewell/amphtml,jpettitt/amphtml,prateekbh/amphtml,cory-work/amphtml,adup-tech/amphtml,taboola/amphtml,jridgewell/amphtml,yandex-pcode/amphtml,alanorozco/amphtml,Gregable/amphtml,ampproject/amphtml,rsimha-amp/amphtml,yandex-pcode/amphtml,jridgewell/amphtml,smartadserver/amphtml,jmadler/amphtml,smartadserver/amphtml,jmadler/amphtml,zhouyx/amphtml,media-net/amphtml,taboola/amphtml,media-net/amphtml,jmadler/amphtml,mhc-gh/amphtml,smartadserver/amphtml,voyagegroup/amphtml,mhc-gh/amphtml,Gregable/amphtml,danielrozenberg/amphtml,Gregable/amphtml,media-net/amphtml,prateekbh/amphtml,Gregable/amphtml,honeybadgerdontcare/amphtml,sharethrough/amphtml,jpettitt/amphtml,media-net/amphtml,danielrozenberg/amphtml,mhc-gh/amphtml,nexxtv/amphtml,cory-work/amphtml,smartadserver/amphtml,Gregable/amphtml,jmadler/amphtml,voyagegroup/amphtml,danielrozenberg/amphtml,ampproject/amphtml,adup-tech/amphtml,nexxtv/amphtml,jpettitt/amphtml,voyagegroup/amphtml,media-net/amphtml,lannka/amphtml,rsimha-amp/amphtml,ampproject/amphtml,taboola/amphtml,mhc-gh/amphtml,rsimha-amp/amphtml,Gregable/amphtml,nexxtv/amphtml,smartadserver/amphtml,yandex-pcode/amphtml,cory-work/amphtml,prateekbh/amphtml,jpettitt/amphtml,honeybadgerdontcare/amphtml,honeybadgerdontcare/amphtml,yandex-pcode/amphtml