Google Chrome browser auto-updates whenever new versions become available, and so are the extensions that you may have installed. Unlike other browsers, that offer you the choice between auto-update and manual update, Google forces the updates upon its users to minimize risk of using out-of-date and possibly vulnerable versions of their software (there is a way to override this, if you are interested).
When the core files of the browser updates a small indicator appears at the position of the wrench icon in the toolbar. It serves to alert the user that the update has been completed and the user should restart the browser so that the updated files could load. But there is no such alerts for updated extensions.
This can be easily fixed with the Update Notifier extension. This extension brings notifications of updated Chrome extensions.
The notification window displays the old version number, the new version number, link to the extension’s homepage, link to the options page if exists and link to launch the application.
And of course, Update Notifier auto-updates itself.