I believe you have to install WebRep in Chrome manually.
Find .crx file in Avast folder (WebRep subfolder) in Program Files and drag and drop .crx
file onto open Chrome while Extensions tab is open.
Before you do that,you should enable everything under Avast settings - WebRep & Antiphishing tab.
BTW, I don't use WebRep,I am using WOT.
Hope this helps.