Does Google ensure that a packaged app is not tampered with?

I'm wondering if a chrome app I upload to the Chrome Webstore could potentially be manipulated (even by Google itself) without users downloading the app noticing it.

I just downloaded a packaged app to check if I can inspect its source code but it didn't allow me to. Is this true for all apps? If the source is hidden, how can I make sure that the app is in its original state?

Edit: I'm not asking about a chrome extension. I know that those can be signed.