code: public void extendDuration(int extend) {
          int passed = timePassed();
          mDuration = passed + extend;
          mDurationReciprocal = 1.0f / mDuration;
          mFinished = false;
      }
docs: Extend the scroll animation. This allows a running animation to scroll
  further and longer, when used with {@link #setFinal(float)}.
  
  @param extend Additional time to scroll in milliseconds.
  @see #setFinal(float)