Flash the light white when vision is locked

Flashing is easier to see, and we need feedback.

Change-Id: I5e827912947e7068feccafdc46eec49374087db8
diff --git a/y2019/control_loops/superstructure/superstructure.h b/y2019/control_loops/superstructure/superstructure.h
index 626c84b..2df9026 100644
--- a/y2019/control_loops/superstructure/superstructure.h
+++ b/y2019/control_loops/superstructure/superstructure.h
@@ -50,6 +50,8 @@
 
   CollisionAvoidance collision_avoidance_;
 
+  int line_blink_count_ = 0;
+
   static constexpr double kMinIntakeAngleForRollers = -0.7;
 
   DISALLOW_COPY_AND_ASSIGN(Superstructure);