mtpd: remove glib and dbus-c++ dependency

Refactors a few things to remove dependencies:
* Move our D-Bus bindings from dbus-c++ to libbrillo
* Move our D-Bus binding generator from xml2cpp to
  chromeos-dbus-bindings
* Move all remaining uses of glib and its message loops
  to libchrome message loops.

BUG=chromium:757584
TEST=emerge, unit tests, connect MTP device to DUT and verify
  that the files app opens up and I can get images

Change-Id: I5483b1da74975daea07d443f7b5c97da67b7b764
Reviewed-on: https://chromium-review.googlesource.com/627261
Commit-Ready: Eric Caruso <ejcaruso@chromium.org>
Tested-by: Eric Caruso <ejcaruso@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
10 files changed