function ScrollbarState(arrowSize, scrollbarSize, oppositeScrollbarSize) {
            this._scrollbarSize = Math.round(scrollbarSize);
            this._oppositeScrollbarSize = Math.round(oppositeScrollbarSize);
            this._arrowSize = Math.round(arrowSize);
            this._visibleSize = 0;
            this._scrollSize = 0;
            this._scrollPosition = 0;
            this._computedAvailableSize = 0;
            this._computedIsNeeded = false;
            this._computedSliderSize = 0;
            this._computedSliderRatio = 0;
            this._computedSliderPosition = 0;
            this._refreshComputedValues();
        }
The minimal size of the slider (such that it can still be clickable) -- it is artificially enlarged.