This implements byte-for-byte update check for service worker scripts imported by importScripts().
Currently, service workers update only when the service worker main script has changes. This does not only conform to the latest spec, but also this is forcing web developers to invest time for workarounds, such as adding hashes to the imported script’s urls to make some update to the main script. Also, some sites are trying to import scripts always from the network by adding random suffix to the url due to this wrong update behavior of imported scripts, but we are planning to deprecate it soon since it can negatively impact the workers’ performance (“Intent to Deprecate and Remove: importScripts() of new scripts after service worker installation” https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/a6P-niHWgF4/CtJEHCnKDwAJ).
Explainers: https://w3c.github.io/ServiceWorker/#update-algorithm