Revert "[Quarantine] Attach source metadata to files only on Windows and Mac."

This reverts commit 10156ea4faa45bc0a61817c07659dc4c98ce910b.

Reason for revert: Appears to introduce failures to PPAPIFileChooserTest.FileChooser_Quarantine. crbug.com/927074

Original change's description:
> [Quarantine] Attach source metadata to files only on Windows and Mac.
> 
> This change stops attaching the origin and referrer URL metadata to
> downloaded files on Linux. This information was previously set via the
> user.xdg.origin.url and user.xdg.referrer.url xattrs. Attaching this
> metadata doesn't provide any security guarantees on Linux, and is a
> privacy risk.
> 
> R=​wfh@chromium.org
> 
> Bug: 917842
> Change-Id: If0586d9b1c340f51ebc480f3c2281cc17e478c5e
> Reviewed-on: https://chromium-review.googlesource.com/c/1407441
> Commit-Queue: Asanka Herath <asanka@chromium.org>
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Reviewed-by: Will Harris <wfh@chromium.org>
> Reviewed-by: Min Qin <qinmin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#627488}

TBR=avi@chromium.org,qinmin@chromium.org,wfh@chromium.org,asanka@chromium.org

Change-Id: I7af4d25a06453ee1c83864b0e3ed9bd736b050ed
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 917842
Reviewed-on: https://chromium-review.googlesource.com/c/1447035
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Joshua Pawlicki <waffles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627609}
10 files changed