Seems like there is nothing wrong. With the latest update Avast did away with the WebRep plugin and Avast Online Security took over. You should now see an “a” on the top left of your Chrome web browser. Its a bug that Avast shows it not installed but clearly it is. If you click on “install” you will be brought to a web page to install Avast Online Security. So technically there is no issue. Do a Google search and you will see the webrep rating system. No reason to be alarmed my friend.
https://chrome.google.com/webstore/search-extensions/avast?utm_source=chrome-ntp-icon
Read up on it.