GitLab

This is a reland of 00437792

The main difference is to make sure iterating over a directory doesn't
return files we don't want to expose either (and not CHECK failing if
such files are found when iterating).

Original change's description:
> [FSA] Add IsSafePathComponent checks to GetFile/GetDirectoryHandle.
>
> This isn't directly using net::IsSafePortablePathComponent since what
> is safe for the File System Access API is not the same as what is safe
> for Downloads. As such currently this duplicates a lot of the
> implementation of this method, but in a followup we should attempt to
> unify these two implementations as much as possible.
>
> Bug: 1150810, 1154757
> Change-Id: Iba4c92ef5f1cd924aa22b9dd201762d48b4bbc3b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568383
> Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
> Reviewed-by: Victor Costan <pwnall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#833042}

Bug: 1150810
Bug: 1154757
Change-Id: I3341b9824a1ac4cbd6f100355960ad55b01f0753
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2575370
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834118}