Ext Tab下Grid配置autoScroll时浏览器不显示滚动条的问题

配置tab下items layout:'fit'

示例

  var tabPanel = Ext.create('Ext.tab.Panel', {
            region: 'center',
            items: [{
                title: '001',
                items: 001Grid,
                layout:'fit'
            }, {
                title: '002'
            }, {
                title: '003'
            }, {
                title: '004'
            }]      
        });