Postman founder here. We saw this coming a while back. Chrome apps have had several issues related to window switching and menu control. We have been waiting for a fix for these for ages but they never came. We decided to build a cross platform app based on Electron last year and now have apps on OS X and Windows [1] with Linux coming soon.
This is not the first time Google has deprecated things or made a drastic change in the Chrome platform. Postman had to shift from the legacy style apps to the packaged style apps in 2014 while it still had hundreds of thousands of users on the legacy platform. Google's solution for the transition is pretty bad. You upload a new zip file and everyone sees the new app running outside the browser and without the ability to do certain things. This transition system was not available when the Chrome app platform launched and we had to create a new listing. Other apps that transitioned their users to the new platform on the existing listing got hammered in ratings as people were pretty obviously pissed.
1. Postman apps: www.getpostman.com/apps