I\'m trying to create a Chrome package App with an icon in the system menu bar as explain here : https://docs.google.com/document/d/1QhhfR33Y28Yqnnoa_Sl3fnZK_mKtwt4dZe6kNyJ_
The hangouts app uses a "panel" type window to achieve its behaviour, see Abraham's answer on How to build an chrome extension like Google Hangouts. Essentially, when you open a window, add type="panel" parameter:
chrome.windows.create({ url: 'https://mobile.twitter.com/', type: 'panel' });
Regarding the error you mentioned, this is because you are using the Beta Chrome build, and it has realised that the feature is not available in this version, and is advising you that you need a dev channel or trunk release. Find out more about Chrome release channels here: http://www.chromium.org/getting-involved/dev-channel