How to revert a dismissed javascript popup alert box in chrome?

When Google Chrome blocks pop-ups for you, the blocked pop-up alert icon appears in the address bar. If you click on the icon, you can see the pop-ups that have been blocked for that page. If you'd like to allow pop-ups for that specific site:
1. Click the pop-up alert icon  (in the address bar).
2. Click the link for the pop-up you'd like to see.
3. To always see pop-ups for the site, select "Always show pop-ups from [site]." 

If you'd like to proactively allow pop-ups for specific sites:
1. Click the Chrome menu   in the top right hand corner of your browser.
2. Select Settings.
3. Click Show advanced settings
4. Under the "Privacy" section, click the Content settings button.
5. In the "Pop-ups" section, select "Do not allow any site to show pop-ups." 
6. Click the 'Manage exceptions' button.
7. Type in the url of the site that you'd like to allow pop-ups from.