Add loop timing to IterativeRobot and TimedRobot (#781)

wpilibc/src/main/native/include/TimedRobot.h

@@ -33,36 +33,27 @@ class TimedRobot : public IterativeRobotBase, public ErrorBase {
   void StartCompetition() override;
 
   /**
-   * Set time period between calls to Periodic() functions.
-   *
-   * A timer event is queued for periodic event notification. Each time the
-   * interrupt occurs, the event will be immediately requeued for the same time
-   * interval.
-   *
-   * @param period Period in seconds.
-   */
-  void SetPeriod(double seconds);
-
-  /**
-   * Get time period between calls to Periodic() functions.
+   * Get the time period between calls to Periodic() functions.
    */
   double GetPeriod() const;
 
- protected:
-  TimedRobot();
+  /**
+   * Constructor for TimedRobot.
+   *
+   * @param period Period in seconds.
+   */
+  explicit TimedRobot(double period = kDefaultPeriod);
+
   ~TimedRobot() override;
 
  private:
-  // Prevents loop from starting if user calls SetPeriod() in RobotInit()
-  bool m_startLoop = false;
-
   HAL_NotifierHandle m_notifier{0};
 
   // The absolute expiration time
   double m_expirationTime = 0;
 
   // The relative time
-  double m_period = kDefaultPeriod;
+  double m_period;
 
   /**
    * Update the HAL alarm time.