Right now, this is available in Chrome Beta only, but it should find its way to the regular Chrome app soon enough.
Not everyone likes this feature, though. For people who like to keep tabs on their open tabs (pun not intended!), it can be difficult to manage previous tabs when they intermingle with previously open apps.
Luckily, this feature is easy to opt out of, if you fall into this camp. Simply open up the Chrome browser, navigate to settings, and select Merge tabs and apps. Turn it off, and your tabs will live only in the Chrome browser going forward.