add text in google chrome extension icon

I want to add a text showing the minutes spent by the user in the running activity in my Google Chrome extension that called开发者_开发知识库 pharaohs Time tracker can see it here https://chrome.google.com/extensions/developer/edit/cegaadncabdacaplfeondbaodibgjfhi?hl=en

I can't find anything in there API although a lot of people using it like ext called go to IMDB

You can overlay a badge on your browser action by calling chrome.browserAction.setBadgeText (see also chrome.browserAction.setBadgeBackgroundColor to style the badge).