Add locked target info to position visualizer.

Change-Id: I31ece9023dccd2126eb50ea6601b3a70d850906f
diff --git a/y2019/vision/server/server.cc b/y2019/vision/server/server.cc
index 1ed6ac9..0253a4c 100644
--- a/y2019/vision/server/server.cc
+++ b/y2019/vision/server/server.cc
@@ -159,6 +159,13 @@
       stream << "\"x\": " << drivetrain_status->x << ",";
       stream << "\"y\": " << drivetrain_status->y << ",";
       stream << "\"theta\": " << drivetrain_status->theta;
+      if (drivetrain_status->line_follow_logging.frozen) {
+        stream << "\"target\": {";
+        stream << "\"x\": " << drivetrain_status->line_follow_logging.x << ",";
+        stream << "\"y\": " << drivetrain_status->line_follow_logging.y << ",";
+        stream << "\"theta\": " << drivetrain_status->line_follow_logging.theta;
+        stream << "}\n";
+      }
       stream << "}\n";
 
       stream << "}";