Ensure embedded and twa start-urls match (#440)
Ensure embedded and twa start-urls match (#440)

* Ensure embedded and twa start-urls match

* Throws error when missing webManifestUrl

- Removing the check makes the linter unhappy.
- We could use the `!.` notation, but throwing a more clear error
  message is better.
GoogleChromeLabs/bubblewrap,GoogleChromeLabs/bubblewrap,GoogleChromeLabs/bubblewrap,GoogleChromeLabs/bubblewrap