Manage monotonic offsets correctly in y2020 localizer

Currently only supports a single pi, but expanding to pi[2-5] shouldn't
be difficult.

Change-Id: Ibed8bd5a59e1a5a9971e9b60c81da413c21b4f7e
diff --git a/y2020/control_loops/drivetrain/localizer.h b/y2020/control_loops/drivetrain/localizer.h
index 0b79361..8636a7a 100644
--- a/y2020/control_loops/drivetrain/localizer.h
+++ b/y2020/control_loops/drivetrain/localizer.h
@@ -3,6 +3,7 @@
 
 #include "aos/containers/ring_buffer.h"
 #include "aos/events/event_loop.h"
+#include "aos/network/message_bridge_server_generated.h"
 #include "frc971/control_loops/drivetrain/hybrid_ekf.h"
 #include "frc971/control_loops/drivetrain/localizer.h"
 #include "y2020/control_loops/superstructure/superstructure_status_generated.h"
@@ -86,6 +87,8 @@
   std::vector<aos::Fetcher<frc971::vision::sift::ImageMatchResult>>
       image_fetchers_;
 
+  aos::Fetcher<aos::message_bridge::ServerStatistics> clock_offset_fetcher_;
+
   // Buffer of recent turret data--this is used so that when we receive a camera
   // frame from the turret, we can back out what the turret angle was at that
   // time.