Implmented ZeroOuputs function for the drivetrain.

Change-Id: I0e35f34ce3c2d7548775aed20e6596168a806e88
diff --git a/frc971/control_loops/drivetrain/drivetrain.h b/frc971/control_loops/drivetrain/drivetrain.h
index a2f2015..30548be 100644
--- a/frc971/control_loops/drivetrain/drivetrain.h
+++ b/frc971/control_loops/drivetrain/drivetrain.h
@@ -21,17 +21,20 @@
  public:
   // Constructs a control loop which can take a Drivetrain or defaults to the
   // drivetrain at frc971::control_loops::drivetrain
-  explicit DrivetrainLoop(const DrivetrainConfig &dt_config,
+  explicit DrivetrainLoop(
+      const DrivetrainConfig &dt_config,
       ::frc971::control_loops::DrivetrainQueue *my_drivetrain =
           &::frc971::control_loops::drivetrain_queue);
 
  protected:
   // Executes one cycle of the control loop.
-  virtual void RunIteration(
+  void RunIteration(
       const ::frc971::control_loops::DrivetrainQueue::Goal *goal,
       const ::frc971::control_loops::DrivetrainQueue::Position *position,
       ::frc971::control_loops::DrivetrainQueue::Output *output,
-      ::frc971::control_loops::DrivetrainQueue::Status *status);
+      ::frc971::control_loops::DrivetrainQueue::Status *status) override;
+
+  void Zero(::frc971::control_loops::DrivetrainQueue::Output *output) override;
 
   typedef ::aos::util::SimpleLogInterval SimpleLogInterval;
   SimpleLogInterval no_position_ = SimpleLogInterval(