crash: Update list_proxies to call new D-Bus service.

Update crash-reporter's list_proxy program to call Chrome's
new org.chromium.NetworkProxyService D-Bus service rather
than org.chromium.LibCrosService. Also drop XML bindings and
use async method calls instead of the old, more-complicated
signal-requesting approach.

BUG=chromium:446115,chromium:703217
TEST=ran it after configuring Chrome to use direct
     connections or a PAC file and verified that correct
     connection info was printed

Change-Id: I17202e7fb917f73956a7c6c514b1adc584ffd258
Reviewed-on: https://chromium-review.googlesource.com/487732
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
2 files changed