As the following figure shows, if you already have a web app, you don't need to change it; you can just publish it as a hosted app. If you're willing to modify your app or build one from scratch, you have more options.
* 10MB is the current size limit for packaged apps. If your app (with all its essential assets) can't fit into a 10MB ZIP file, then your app is too big to be a packaged app.
If you're having trouble deciding what type of app to create, read the article Extensions, Packaged Apps, and Hosted Apps in the Chrome Web Store. Here's some additional information to help you choose:
Rule of thumb: A packaged app should feel like a hosted app, not like an extension.