GitLab

If the SafeBrowsing service couldn't come up with a definite verdict for
some reason (e.g. couldn't reach the backend or encountered some error)
it would default to a verdict of SAFE. This in turn could cause a
download that would've been considered dangerous due its file type to be
considered safe. This change introduces an UNKNOWN verdict that the
SafeBrowsing service can use to indicate that a verdict couldn't be
determined.

Downloads then uses that signal to revert to the old behavior of
displaying a dangerous downloads warning based on the file type.

BUG=269157

Review URL: https://codereview.chromium.org/565053002

Cr-Commit-Position: refs/heads/master@{#295167}