为什么Chrome需要机器人。txt?

我在日志中注意到,Chrome要求 robots.txt

[...]
2017-09-17 15:22:35 - (sanic)[INFO]: Goin' Fast @ http://0.0.0.0:8080
2017-09-17 15:22:35 - (sanic)[INFO]: Starting worker [26704]
2017-09-17 15:22:39 - (network)[INFO][127.0.0.1:36312]: GET http://localhost:8080/  200 148
2017-09-17 15:22:39 - (sanic)[ERROR]: Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/sanic/app.py", line 493, in handle_request
    handler, args, kwargs, uri = self.router.get(request)
  File "/usr/local/lib/python3.5/dist-packages/sanic/router.py", line 307, in get
    return self._get(request.path, request.method, '')
  File "/usr/local/lib/python3.5/dist-packages/sanic/router.py", line 356, in _get
    raise NotFound('Requested URL {} not found'.format(url))
sanic.exceptions.NotFound: Requested URL /robots.txt not found

2017-09-17 15:22:39 - (network)[INFO][127.0.0.1:36316]: GET http://localhost:8080/robots.txt  404 42
[...]

我正在运行Chromium:

60.0.3112.113 (Developer Build) Built on Ubuntu, running on Ubuntu 16.04 (64-bit)

为什么会这样? 有人能详细说明一下吗?