The feature notifies users about what their extensions are up to
The latest Chrome dev update has enabled the extension activity notification feature that Google's been working on for a while. You'll notice next to the bookmark star button an indicator of how many extensions are interacting with the page you're currently visiting.It's a great way of knowing just what extension is doing what. Users implicitly trust extensions, the fact that they're coming from the Chrome Web Store helps with that, but that doesn't mean that trust can't be abused.
Until now, there was little way of knowing whether an extension did just what it was supposed to do or not. The indicator will list all the extensions currently in use on that page.
Clicking on any of the extensions there will redirect users to the extensions settings page. Google is also working on an activity log page for extensions, which will keep track of all of the actions performed.
The feature is not enabled by default, you can enable the activity page from chrome://flags, search for "Enable extension activity UI."