Add Linux file chooser dialog.

This will be used to allow the user to select a file to download from
the host to the client.

Bug: 679313
Change-Id: I7e3e2d1c1de1b0c415af3560ab1d60fb7d3fde7e
Reviewed-on: https://chromium-review.googlesource.com/c/1419038
Commit-Queue: Erik Jensen <rkjnsn@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627254}
5 files changed