不可行权限判断API：

context.checkCallingPermission

context.checkCallingOrSelfPermission

context.checkSelfPermission

PermissionChecker.checkSelfPermission

使用Camera中的mHasPermission

private boolean cameraHasPermission(Camera camera) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
    if ((Build.VERSION.SDK_INT < Build.VERSION_CODES.M){
        Class clazz = Class.forName(camera.getClass().getCanonicalName());
        Field mHasPermission = clazz.getDeclaredField("mHasPermission");
        mHasPermission.setAccessible(true);
        return mHasPermission.getBoolean(camera);
    }
}