The `Cache.addAll()` API allows multiple entries to be added to the cache at once. The spec requires that each request/response pair avoid overwriting another entry being added in the same call. Previously chrome would resolve such conflicts by storing the later entry and ignoring the earlier entry. This feature is to fix this behavior and properly reject with InvalidStateError.
Docs: https://developer.mozilla.org/en-US/docs/Web/API/Cache/addAll