code: function(downHight, downOffset) {
              // 复用default的同名函数代码
              this._super(downHight, downOffset);
              
              var rate = downHight / downOffset,
                  degree = DRAWER_FULL_DEGREE * (1 - Math.min(rate, 1));
              
              this._transformDrawer(degree);
          }
docs: 重写下拉过程动画
  @param {Number} downHight 当前下拉的高度
  @param {Number} downOffset 下拉的阈值