Choreographer
Logcat使用关键词Choreographer进行过滤，对App做一些操作，一般能看到控制台输出日志：
I/Choreographer: Skipped 55 frames! The application may be doing too much work on its main thread.
I/Choreographer: Skipped 43 frames! The application may be doing too much work on its main thread.
观察App掉帧一种方式，默认打印掉帧>=30帧的信息。已ROOT手机可以修改。
分析调用过程、帧率统计、分析Systrace
硬件每16ms产生一个VSync信号，App要想实现垂直同步，收到VSync只要调用DisplayEventReceiver的nativeScheduleVsync方法后，才能收到下一个VSync请求Vsync只是单次调用。
