update_engine: Migrate UE DBus service to chrome DBus bindings.

chromeos-dbus-bindings now generates the adaptor interface that
update_engine exposes over DBus. This interface is implemented in
dbus_service.{h,cc}, which now has a UpdateEngineService class
encapsulating all the service methods implementation.

This allows to write unit test for those methods, which are included
in this CL for all the non-trivial methods.

This CL now uses chrome's DBus bindings for the update_engine serive,
but the proxy interaction is still done using dbus-glib. The main loop
in the main.cc file is now replaced with the chromeos::Dameon, which
uses a chromeos::BaseMessageLoop instead of a GlibMessageLoop. This
causes the asynchronous interactions in the proxy side to not work,
which will be fixed in the next CL.

CQ-DEPEND=CL:290990,CL:291092,CL:293334
BUG=chromium:419827
TEST=Added unittest for all dbus_service methods. deployed and tested manually that update_engine dbus interface works.

Change-Id: I6a6d142b2ac1a61a4c3abcb927665b26114abe5c
Reviewed-on: https://chromium-review.googlesource.com/225324
Reviewed-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index ff64128..5131239 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -37,7 +37,8 @@
  protected:
   void SetUp() override {
     loop_.SetAsCurrent();
-    subprocess_.Init();
+    async_signal_handler_.Init();
+    subprocess_.Init(&async_signal_handler_);
   }
 
   // DoTest with various combinations of do_losetup, err_code and
@@ -48,6 +49,7 @@
   static const char* kImageMountPointTemplate;
 
   chromeos::GlibMessageLoop loop_;
+  chromeos::AsynchronousSignalHandler async_signal_handler_;
   Subprocess subprocess_;
 };