Re-land Move ScopedFileDescriptor to dbus/file_descriptor.h

Re-land Move ScopedFileDescriptor to dbus/file_descriptor.h

ScopedFileDescriptor was initially introduced to facilitate the
management of a 'lifeline' FD used when asking permission_broker to
open a port in the device's firewall on CrOS.  It's actually a scoped
wrapper around DBus::FileDescriptor, not a platform file descriptor. I
would like to use it to facilitate some other similar functionality in
which I create a pipe and pass one end over DBus, so it seems like a
good idea to move ScopedFileDescriptor into the dbus library directly.

This reverts commit ee9dc849ffa2df2820381c31d5ba8200774d287a.

BUG=chromium:481340
TEST=FirewallHole unit tests still pass
TBR=stevenjb, reillyg, keybuk

Committed: https://crrev.com/610c3173c4dc2258c10c8b211ab9cbe21f2a1402
Cr-Commit-Position: refs/heads/master@{#327141}

[Chris Masone, 2015-04-27 20:28:16]

cmasone@chromium.org changed reviewers:
+ spang@chromium.org

[Chris Masone, 2015-04-27 20:28:17]

While I'm trying to validate this locally, can you do me a solid and test this
real quick in your build env?

[Chris Masone, 2015-04-27 20:34:50]

cmasone@chromium.org changed reviewers:
+ keybuk@chromium.org, reillyg@chromium.org, stevenjb@chromium.org

[Chris Masone, 2015-04-27 20:35:37]

ok, I've verified that this works in the component build locally.

Since the change was removing an incorrectly added and unneeded 'visibility'
attribute, TBR'ing to the people who already LGTM'd the previous version of this
CL.

LGTY, spang?

[spang, 2015-04-27 20:46:40]

tested & lgtm.

Thank you!

[Chris Masone, 2015-04-27 21:35:34]

The CQ bit was checked by cmasone@chromium.org

[commit-bot: I haz the power, 2015-04-27 21:36:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1108083003/1

[commit-bot: I haz the power, 2015-04-27 21:41:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-27 21:42:40]

Patchset 1 (id:??) landed as
https://crrev.com/610c3173c4dc2258c10c8b211ab9cbe21f2a1402
Cr-Commit-Position: refs/heads/master@{#327141}