出處：http://docs.sencha.com/extjs/4.2.1/extjs-build/examples/layout-browser/layouts/combination.js
// A common mistake when adding grids to a layout is creating a panel first,
// then adding the grid to it. GridPanel (xtype:'grid') is a Panel subclass,
// so you can add it directly as an item into a container. Typically you will
// want to specify layout:'fit' on GridPanels so that they'll size along with
// their container and take up the available space.
大致意思是Grid是Panel的子類，不需要用Panel再包Grid了，這樣做的話，會導致Grid的Fit佈局，不能奏效了。
示例頁面：http://docs.sencha.com/extjs/4.2.1/extjs-build/examples/layout-browser/layout-browser.html
選左邊樹上的Combination Examples下的Tabs With Nested Layouts
選Foo頁的Inner Tab 2，這下邊有個“下置標籤選項卡”，再選擇“Nested Grid”，就能Grid自適應的效果。
注意：因為Panel有closable屬性，Grid是子類，當然也有啦。原來Grid也是可以“關閉”的啊！