Add ability to wait for a distance along a spline in auto

Change-Id: I0e992ccffeca59a655b8b890942aa7aaadfb9fd7
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/frc971/control_loops/drivetrain/splinedrivetrain.cc b/frc971/control_loops/drivetrain/splinedrivetrain.cc
index 0f9418c..ddcf63d 100644
--- a/frc971/control_loops/drivetrain/splinedrivetrain.cc
+++ b/frc971/control_loops/drivetrain/splinedrivetrain.cc
@@ -256,6 +256,8 @@
           ? CHECK_NOTNULL(current_trajectory())->length() - current_xva_.x()
           : 0.0);
   trajectory_logging_builder.add_available_splines(handles_vector);
+  trajectory_logging_builder.add_distance_traveled(
+      executing_spline_ ? current_xva_.x() : 0.0);
 
   return trajectory_logging_builder.Finish();
 }