If a download ends with CONTENT_LENGTH_MISMATCH error, chrome treat it as completed.
However, this could happen if server closes the connection too early.
And it causes the downloaded file size to be incorrect.
And with pause/resume functionalities, this could happen more frequently.
This change treats these download as interrupted if strong validators are present.
For downloads without strong validators, auto resumption could cause them to enter a restart->interrupt->restart cycle.
As a result, download is treated as completed if there are no strong validators.

BUG=453357

Review-Url: https://codereview.chromium.org/2832223004
Cr-Commit-Position: refs/heads/master@{#467897}