Earlier quoted context omitted.
With regard to resumable downloads -- that "cleverness" isn't for the sake of being clever; it's in there to avoid two very common cases where a naïve download resume will corrupt a file: 1. The remote file has changed since the previous download, so "resuming" the download will end up combining two different files. 2. The user's computer crashed during the first download, and some of the data in the partial download…
1. Date / file size check. In doubt, ask the user. 2. Rollback a few megabytes. These problems were solved ages ago by most download managers.
Indeed, this was already proposed on the bug tracker, but the Chromium developers ignored it: https://bugs.chromium.org/p/chromium/issues/detail?id=7648#c...