SurfaceControl 和 Surface
Surface 对象使应用能够渲染要在屏幕上显示的图像。通过 SurfaceHolder 接口，应用可以编辑和控制 Surface。
public final class ViewRootImpl implements ViewParent, ... {
...
public final Surface mSurface = new Surface();
private final SurfaceControl mSurfaceControl = new SurfaceControl();
...
}