GitLab

This was only implemented half-way, and the file picker still limited
choices to directories.  So this code only got run (incorrectly)
by selecting a folder that ends in .zip (which happens on ChromeOS
for a mounted zip archive).

BUG=418753

Review URL: https://codereview.chromium.org/676503003

Cr-Commit-Position: refs/heads/master@{#301141}