I’d like to use new APIs provided for Chrome Packaged Apps, but also want to preserve ability to open some local URL in my current browser environment, is it possible? All Packaged Apps tutorials are focused on creating separate window and using app as first class citizen in the system.
Maybe its possible somehow to use chrome.socket and other APIs as usual, probably even only in developer mode?
No, it is not possible by design. Chrome packaged apps run separately from the browser and have no access to browser-specific features, like tabs. The closest you can get is to open an external (not in the packaged app) URL in the browser through window.open.
However, you can kind of emulate a browser by using the webview tag. See the code of the Browser sample to learn how to do it.
You can also install an extension that talks to your packaged app using the just released messaging API. See the messaging sample to learn how – it is pretty simple as long as you know the app and the extension IDs.