public void extendDuration(int extend) {
        int passed = timePassed();
        mDuration = passed + extend;
        mDurationReciprocal = 1.0f / mDuration;
        mFinished = false;
    }
Extend the scroll animation. This allows a running animation to scroll
further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}.

@param extend Additional time to scroll in milliseconds.
@see #setFinalX(int)
@see #setFinalY(int)
menudrawer/src/net/simonvt/menudrawer/Scroller.java