update_engine: Support milestones to EOL from Omaha

Initiative to show EOL message on Chrome OS devices require that
update_engine parses the fields within Omaha response that pertain to the
new milestones to EOL field. The Omaha response will include a new
field called "milestones_to_eol" which will be an integer value
string.

The job of update_engine when it comes to milestones to EOL from Omaha
is to merely forward. No checks and no modifications of fields are
done within update_engine besides being able to convert the milestones
to EOL from a string to integer.

BUG=chromium:994999
TEST=FEATURES="test" emerge-$BOARD update_engine update_engine-client
TEST=cros deploy $IP update_engine update_engine-client
TEST=test_that -b $BOARD $IP autoupdate_EOL # from Cq-Depend
TEST=test_that -b $BOARD $IP autoupdate_EOL.milestones # from Cq-Depend

Cq-Depend:chromium:1761371
Change-Id: I268e4c8e641b17d6a727a50f53285cc97c76eb22
Reviewed-on: https://chromium-review.googlesource.com/1759285
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Nicolas Norvez <norvez@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/dbus_service.cc b/dbus_service.cc
index b379603..168265d 100644
--- a/dbus_service.cc
+++ b/dbus_service.cc
@@ -212,8 +212,9 @@
 }
 
 bool DBusUpdateEngineService::GetEolStatus(ErrorPtr* error,
-                                           int32_t* out_eol_status) {
-  return common_->GetEolStatus(error, out_eol_status);
+                                           int32_t* out_eol_status,
+                                           int32_t* out_milestone_to_eol) {
+  return common_->GetEolStatus(error, out_eol_status, out_milestone_to_eol);
 }
 
 UpdateEngineAdaptor::UpdateEngineAdaptor(SystemState* system_state)