"Safari" would like to control this computer using accessibility features

I recently did a clean install of OS X Yosemite 10.10.2 on my MacBook Air.

I was making a credit card payment on the Barclaycard website and received a dialog window saying ""Safari" would like to control this computer using accessibility features."

I chose "Deny" but I am wondering why I received this dialog in the first place? I am certain I was on the actual, official Barclaycard website. Do I have malware? The only extensions I am using with Safari are AdBlock and 1Password.