chromium/extensions/test/data/content_hash_fetcher/zero_byte_file/README.txt

The files in this directory came from downloading a test extension from the
webstore* that had properly signed verified_contents.json file, taking all
extension files (including _metadata/verified_contents.json and
_metadata/computed_hashes.json) from the .crx and putting them into
source.zip file.

Among other files, the extension contains a 0 byte background.js file.

* https://chrome.google.com/webstore/detail/ajcpkmldgikjjbikbkoleifacehapefj