code: function ListView_getViewportSize() {
                      if (this._viewportWidth === _Constants._UNINITIALIZED || this._viewportHeight === _Constants._UNINITIALIZED) {
                          this._viewportWidth = Math.max(0, _ElementUtilities.getContentWidth(this._element));
                          this._viewportHeight = Math.max(0, _ElementUtilities.getContentHeight(this._element));
                          this._writeProfilerMark("viewportSizeDetected width:" + this._viewportWidth + " height:" + this._viewportHeight);
  
                          this._previousWidth = this._element.offsetWidth;
                          this._previousHeight = this._element.offsetHeight;
                      }
                      return {
                          width: this._viewportWidth,
                          height: this._viewportHeight
                      };
                  }
docs: Methods in the site interface used by ScrollView