Update to use libbrillo Chrome proxy resolver

This uses the new proxy resolution code in libbrillo for doing proxy
resolution rather than making the D-Bus calls directly through the
generated bindings. The unittest for this class was removed since the
main function of it was removed. It now is essentially just a wrapper
around the call into libbrillo along with some minimal code for
allowing cancelling of callbacks.

BUG=chromium:771386
TEST=Unit tests pass

Change-Id: Ib0d4e413482f4bdfe0e9689f68118efbec94ec9d
Reviewed-on: https://chromium-review.googlesource.com/698964
Commit-Ready: Jeffrey Kardatzke <jkardatzke@google.com>
Tested-by: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Sen Jiang <senj@chromium.org>
diff --git a/update_attempter.h b/update_attempter.h
index 082ebfe..f0747e2 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -48,12 +48,6 @@
 
 class MetricsLibraryInterface;
 
-namespace org {
-namespace chromium {
-class NetworkProxyServiceInterfaceProxyInterface;
-}  // namespace chromium
-}  // namespace org
-
 namespace policy {
 class PolicyProvider;
 }
@@ -70,10 +64,7 @@
   using UpdateStatus = update_engine::UpdateStatus;
   static const int kMaxDeltaUpdateFailures;
 
-  UpdateAttempter(SystemState* system_state,
-                  CertificateChecker* cert_checker,
-                  org::chromium::NetworkProxyServiceInterfaceProxyInterface*
-                      network_proxy_service_proxy);
+  UpdateAttempter(SystemState* system_state, CertificateChecker* cert_checker);
   ~UpdateAttempter() override;
 
   // Further initialization to be done post construction.