[Native File System] Restrict access to sensitive directories.

If the user selects a sensitive directory, a parent of a sensitive directory,
or anything in certain extra sensitive directories, prompt the user to pick
something else.

Bug: 968851
Change-Id: I5ad144f89c823f20e766f463383959bc2a595327
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696183
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678515}
12 files changed