Hide Default title bar in Chrome Packaged App

Question

I am creating a window on the launch app event, How can I be able to hide the default title bar so I can be able to create mine?

from customize title bar in chrome packaged app, it was mentioned that we use frame: none but without showing how to implement it. How can I be able to implement it?

my background.js

chrome.app.runtime.onLaunched.addListener(function() {
    chrome.app.window.create('index.html', {
      id: "main_window",
      'frame': none,
      'outerBounds': {
        'width': 400,
        'height': 500
      },
      'innerBounds':{

      }
    });
  });