Android <include />, <merge /> and <ViewStub />
http://developer.android.com/training/improving-layouts/index.html
提高layout的性能

<include /> --layout component: share and reuse(layout 组件的共享与复用)

<merger />-- layout level: optimize and improve layout time(layout 层次的优化以提高layou的时间从而提高layout 速度)

<ViewStub>-- layout load: 按需加载layout