The Doc says if you want to create a panel window ,you should use
chrome.windows.create({...,type:"panel"}, function callback)
At the same time, it says "Specifies what type of browser window to create. The 'panel' type creates a popup unless the '--enable-panels' flag is set."
So you should go to "chrome://flags" to change it manually. But Google Hangouts can create the panel without doing that. How does it do that?